Double-exciting-coil type induced magnetic field detection device, method and system

Abstract

The invention provides a double-exciting-coil type induced magnetic field detection device, method and system. The induced magnetic field detection device comprises an excitation current source, a magnetic sensor, an excitation magnetic field coil and a compensation magnetic field coil. The excitation magnetic field coil and the compensation magnetic field coil are symmetrical about the magnetic sensor; the excitation current source is used for exciting the excitation magnetic field coil to generate a first excitation magnetic field and is used for exciting the compensation magnetic field coil to generate a second excitation magnetic field; the first excitation magnetic field and the second excitation magnetic field are the same in size and opposite in direction at the position of the magnetic sensor in the Z direction; an object to be measured generates an induced magnetic field under the action of the first excitation magnetic field and the second excitation magnetic field; the magnetic sensor is used for detecting the component of the induced magnetic field in the Z direction. According to the double-exciting-coil type induced magnetic field detection device, the induced magnetic field of the object to be detected can be accurately detected.

Description

Technical Field

[0001] The present application belongs to the technical field of magnetic induction tomography, and relates to a dual-excitation coil type induced magnetic field detection device, method and system. Background Art

[0002] Magnetic induction tomography (MIT) uses inductive sensing coils to map the electromagnetic properties of an object. As a non-invasive, non-nuclear, and non-contact technology, it has broad potential applications in a wide range of problems and industrial challenges, from biomedical imaging to non-destructive testing. Due to its advantages of being non-invasive, non-contact, low-cost, capable of long-term continuous monitoring, and lacking the issue of contact impedance, MIT has recently garnered widespread attention in biomedical imaging fields, including intracranial hemorrhage detection, stroke detection, electromagnetic head imaging, electromagnetic joint imaging, bladder volume monitoring, and breast tumor imaging.

[0003] The basic principles of magnetic induction tomography can be explained using basic mutual induction and eddy current theory. Simply put, passing an alternating current through one or more excitation coils generates a primary magnetic field, which induces an electric field that is detected by one or more measuring coils or magnetic sensors. The induced voltage can be measured from this electric field. If a conductive object is placed in this magnetic field, eddy currents are generated, which in turn generate a magnetic field, called the induced magnetic field. Therefore, the electric field in the measuring coil is partially induced by both the primary and induced magnetic fields. Consequently, the induced voltage in the measuring coil or magnetic sensor will differ depending on whether a conductive object is present in the magnetic field. If no conductive object is present, the induced voltage is entirely due to the primary magnetic field; if an object is present, the induced voltage is due to both the primary and induced magnetic fields. By analyzing the differences in the induced voltages, various properties of the conductive object can be reconstructed.

[0004] Current technology cannot directly obtain the magnetic field strength of the induced magnetic field from the excitation magnetic field. Therefore, how to accurately detect the induced magnetic field strength of the object to be measured has become an urgent problem that needs to be solved. Summary of the Invention

[0005] The purpose of the present application is to provide a dual-excitation coil type induced magnetic field detection device and method for accurately detecting the induced magnetic field of an object to be measured.

[0006] In the first aspect, the present application provides a dual-excitation coil induction magnetic field detection device, which includes: an excitation current source, a magnetic sensor, an excitation magnetic field coil and a compensation magnetic field coil; the excitation magnetic field coil and the compensation magnetic field coil are symmetrical about the magnetic sensor; the excitation current source is used to excite the excitation magnetic field coil to generate a first excitation magnetic field, and is used to excite the compensation magnetic field coil to generate a second excitation magnetic field; at the position of the magnetic sensor, the first excitation magnetic field and the second excitation magnetic field are the same size and opposite direction in the Z direction; the object to be measured generates an induced magnetic field under the action of the first excitation magnetic field and the second excitation magnetic field; the magnetic sensor is used to detect the component of the induced magnetic field in the Z direction.

[0007] In an implementation of the first aspect, the induced magnetic field detection device further includes a signal processing module, wherein the signal processing module is used to extract parameters of the induced magnetic field, and the parameters of the induced magnetic field are used for magnetic induction tomography.

[0008] In an implementation of the first aspect, the parameters of the induced magnetic field are also used to obtain the phase difference between the induced magnetic field at the magnetic sensor and the excitation magnetic field at the center point of the surface of the object to be measured on one side close to the magnetic sensor, and / or to obtain the dielectric constant and / or conductivity of the object to be measured.

[0009] In an implementation of the first aspect, the magnetic sensor includes: a magnetoelectric sensing unit and a charge amplifier; the magnetoelectric sensing unit is fixed on a position control device, and the charge amplifier is connected to the signal processing module; the position control device is used to adjust the position of the magnetoelectric sensing unit.

[0010] In an implementation of the first aspect, the excitation magnetic field coil and the compensation magnetic field coil have the same size and the same number of turns.

[0011] In an implementation of the first aspect, the excitation magnetic field coil and the compensation magnetic field coil are parallel to each other, and the excitation magnetic field coil and the compensation magnetic field coil are coaxially placed directly above the object to be measured.

[0012] In an implementation of the first aspect, a first excitation current flowing into the excitation magnetic field coil and a second excitation current flowing into the compensation magnetic field coil are equal in magnitude and opposite in direction.

[0013] In an implementation of the first aspect, the magnetoelectric sensing unit includes metallic glass and lithium niobate.

[0014] In second aspect, the present application provides a dual-excitation coil type induced magnetic field detection method, the induced magnetic field detection method comprising: generating the first excitation magnetic field and the second excitation magnetic field by the excitation magnetic field coil and the compensation magnetic field coil, the object to be measured generates an induced magnetic field under the action of the first excitation magnetic field and the second excitation magnetic field; detecting the component of the induced magnetic field in the Z direction by the magnetic sensor.

[0015] In a second aspect, the present application provides a dual-excitation coil type induction magnetic field detection system, which includes the above-mentioned dual-excitation coil type induction magnetic field detection device and an imaging module.

[0016] As described above, the dual-excitation coil induction magnetic field detection device and method described in this application have the following beneficial effects:

[0017] This application utilizes dual excitation coils to compensate for the excitation magnetic field of the compensating magnetic field coil. Based on the fact that at the location of the magnetic sensor, the first excitation magnetic field and the second excitation magnetic field are of equal magnitude and opposite direction in the Z direction, thereby reducing the influence of the total magnetic field on the induced magnetic field of the object to be measured, so that the magnetic sensor can directly obtain the magnetic field strength of the induced magnetic field from the excitation magnetic field. The dual excitation coil model of the excitation magnetic field coil and the compensating magnetic field coil, which are symmetrical about the magnetic sensor in the induced magnetic field detection device of this application, improves the detection quality and accuracy of the magnetic field strength of the induced magnetic field and reduces phase noise. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Shown is a structural schematic diagram of the induced magnetic field detection device described in an embodiment of the present application.

[0019] Figure 2 Shown is a schematic diagram of the process of induced magnetic field detection described in an embodiment of the present application.

[0020] Figure 3 Shown is a schematic diagram of the process of induced magnetic field detection described in an embodiment of the present application.

[0021] Figure 4 Shown is a structural schematic diagram of the magnetoelectric sensing unit described in an embodiment of the present application.

[0022] Figure 5 Shown is a structural schematic diagram of an electronic device described in an embodiment of the present application.

[0023] Figure 6 Shown is a structural schematic diagram of the induced magnetic field detection system described in an embodiment of the present application.

[0024] Component number description

[0025] 1 Induction magnetic field detection device

[0026] 11 Excitation current source

[0027] 12 Excitation magnetic field coil

[0028] 13 Compensating magnetic field coil

[0029] 14 Magnetic Sensor

[0030] 15 Signal Processing Module

[0031] 16 Objects to be tested

[0032] 17 Position control device

[0033] 2 Electronic devices

[0034] 21 Memory

[0035] 22 processors

[0036] 23 Display

[0037] 3 Induction magnetic field detection system

[0038] 30 Imaging Module

[0039] Steps S11 to S13 DETAILED DESCRIPTION

[0040] The following describes the embodiments of the present application through specific examples. Those skilled in the art can easily understand the other advantages and effects of the present application from the content disclosed in this specification. The present application can also be implemented or applied through other different specific embodiments. The details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that the following embodiments and features in the embodiments can be combined with each other unless they conflict.

[0041] It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present application. Therefore, the illustrations only show components related to the present application and are not drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component can be changed at will, and the component layout type may also be more complicated.

[0042] Magnetic induction technology, an important detection method based on the principle of electromagnetic induction, has been widely used in various fields in recent years. Its core principle is to induce eddy currents in the object under test through an alternating magnetic field. By detecting the changes in the magnetic field caused by these eddy currents, the physical properties of the object under test, such as conductivity, thickness, or defects, can be analyzed. Magnetic induction tomography (MIT) is a significant advancement in this field. It applies an alternating magnetic field outside the test area and measures the changes in the secondary magnetic field caused by the internal conductivity distribution at the boundary. Combined with advanced reconstruction algorithms, it generates an image of the conductivity distribution of the test area, demonstrating great potential in biomedical and industrial testing. Magnetic induction testing technology evaluates the physical properties of the object under test by measuring changes in the magnetic field. The eddy current magnetic induction testing model, a specific implementation of this technology, uses an excitation coil to generate an alternating magnetic field on or within the object under test, inducing eddy currents. The detection coil then measures the changes in the magnetic field caused by these eddy currents to analyze the object under test.

[0043] Magnetic induction tomography (MIT) uses inductive sensing coils to map the electromagnetic properties of an object. As a non-invasive, non-nuclear, and non-contact technology, it has broad potential applications in a wide range of problems and industrial challenges, from biomedical imaging to non-destructive testing. Due to its advantages of being non-invasive, non-contact, low-cost, capable of long-term continuous monitoring, and lacking the issue of contact impedance, MIT has recently garnered widespread attention in biomedical imaging fields, including intracranial hemorrhage detection, stroke detection, electromagnetic head imaging, electromagnetic joint imaging, bladder volume monitoring, and breast tumor imaging.

[0044] The basic principles of magnetic induction tomography can be explained using basic mutual induction and eddy current theory. Simply put, passing an alternating current through one or more excitation coils generates a primary magnetic field, which induces an electric field that is detected by one or more measuring coils or magnetic sensors. The induced voltage can be measured from this electric field. If a conductive object is placed in this magnetic field, eddy currents are generated, which in turn generate a magnetic field, called the induced magnetic field. Therefore, the electric field in the measuring coil is partially induced by both the primary and induced magnetic fields. Consequently, the induced voltage in the measuring coil or magnetic sensor will differ depending on whether a conductive object is present in the magnetic field. If no conductive object is present, the induced voltage is entirely due to the primary magnetic field; if an object is present, the induced voltage is due to both the primary and induced magnetic fields. By analyzing the differences in the induced voltages, various properties of the conductive object can be reconstructed.

[0045] Some technical solutions use coils as sensing units, but their magnetic field detection sensitivity is low, making direct measurement of the induced magnetic field very difficult. Therefore, it is necessary to increase the excitation magnetic field frequency to the MHz level and use a phase detector to measure the phase difference of the induced voltage of the detection coil relative to the excitation magnetic field to indirectly achieve signal measurement. Magnetic field sensors have the advantages of high sensitivity, ease of integration, small size, and high reliability. However, high sensitivity, wide bandwidth, and low cost are often not achieved simultaneously. The minimum magnetic field detection limit of a fluxgate sensor is close to 1pT, but its bandwidth is only tens of kHz. The minimum magnetic field detection limit of an OPM can reach fT, but its bandwidth is typically only hundreds of Hz, and it requires a near-zero magnetic field environment to operate. The minimum magnetic field detection limit of a superconducting quantum interference device is less than 1fT, and its bandwidth can reach MHz or even higher, but it requires an extremely low temperature environment to operate, and the cryogenic dewar or refrigerator is bulky and expensive.

[0046] Current magnetic field sensor technology solutions, such as fluxgate, OPM, and superconducting quantum interference devices, although they have advantages such as high sensitivity, easy integration, small size, and high reliability, generally have the problem of difficulty in achieving both high sensitivity and wide bandwidth and high cost. At the same time, some sensors require specific environmental conditions (such as extremely low temperatures or near-zero magnetic fields), which limits their application in a wider range of fields. At the same time, it is difficult for current technology to directly obtain the magnetic field strength of the induced magnetic field of the object to be measured from a single excitation magnetic field. Therefore, how to provide an induced magnetic field detection device with high sensitivity, wide bandwidth, low cost, and no need for specific environmental conditions has become an urgent problem to be solved.

[0047] To address at least the above-mentioned issues, the following embodiments of the present application provide a dual-excitation coil induction magnetic field detection device and method. The technical solutions in the embodiments of the present application will be described in detail below in conjunction with the accompanying drawings.

[0048] Figure 1 The structure diagram of the dual excitation coil induction magnetic field detection device in one embodiment of the present application is shown. Figure 1 As shown, the induced magnetic field detection device 1 includes: an excitation current source 11, a magnetic sensor 14, an excitation magnetic field coil 12 and a compensation magnetic field coil 13; the excitation magnetic field coil 12 and the compensation magnetic field coil 13 are symmetrical about the magnetic sensor 14; the excitation current source 11 is used to excite the excitation magnetic field coil 12 to generate a first excitation magnetic field, and is used to excite the compensation magnetic field coil 13 to generate a second excitation magnetic field; the first excitation magnetic field and the second excitation magnetic field are of the same magnitude and opposite directions in the Z direction at the magnetic sensor position 14; the object to be measured 16 generates an induced magnetic field under the action of the first excitation magnetic field and the second excitation magnetic field; the magnetic sensor 14 is used to detect the component of the induced magnetic field in the Z direction.

[0049] Exemplarily, the excitation current source outputs a first excitation signal and a second excitation signal, each of which is an alternating current signal having the same frequency and amplitude but a phase difference of 180°. The first excitation signal generates an excitation magnetic field through the excitation magnetic field coil, and the second excitation signal generates a compensation magnetic field through the compensation magnetic field coil. The object under test generates an induced magnetic field under the influence of the excitation magnetic field generated by the excitation magnetic field coil. Because the excitation magnetic field coil and the compensation magnetic field coil are symmetrical about the magnetic sensor, when excitation signals of equal magnitude and opposite directions are applied to the dual excitation coils of the excitation magnetic field coil and the compensation magnetic field coil, the excitation magnetic field and the compensation magnetic field on the magnetic sensor are equal in magnitude and opposite in direction, and the component of the total excitation magnetic field in the Z direction is zero. At this point, the magnetic sensor is affected only by the induced magnetic field generated by the object under test.

[0050] For example, the object to be tested can be a high conductivity sample such as metal, or a low or high conductivity sample such as physiological saline or biological tissue.

[0051] Exemplarily, the magnetic sensor is positioned directly between the excitation magnetic field coil and the compensation magnetic field coil. At the location of the magnetic sensor, the excitation magnetic field and the compensation magnetic field are equal in magnitude and opposite in direction, canceling each other out. The magnetic sensor primarily detects the induced magnetic field signal and generates an output signal that is transmitted to a signal processing module. The signal processing module extracts the frequency and amplitude of the induced magnetic field signal, and the extracted data is used to generate magnetic induction tomography images.

[0052] In one embodiment of the present application, the excitation magnetic field coil and the compensation magnetic field coil have the same size and the same number of turns. A first excitation current flowing into the excitation magnetic field coil and a second excitation current flowing into the compensation magnetic field coil are equal in size and opposite in direction.

[0053] In one embodiment of the present application, the excitation magnetic field coil and the compensation magnetic field coil are parallel to each other, and the excitation magnetic field coil and the compensation magnetic field coil are coaxially placed directly above the object to be measured.

[0054] In some embodiments, see Figure 2 , taking the salt water to be tested as an example, the center of the upper surface of the salt water to be tested is taken as the coordinate origin O, the number of turns of the excitation magnetic field coil and the compensation magnetic field coil are both N, the height is h, the inner diameter is r1, the outer diameter is r2, the bottom height of the compensation magnetic field coil is z, and the distance between the excitation magnetic field coil and the compensation magnetic field coil is 2c. The magnetic sensor is placed at the center point P(r0,z0) of the excitation magnetic field coil and the compensation magnetic field coil, r0=0, z0=z+h+c. When an AC excitation current I with an angular frequency of ω is applied to the excitation magnetic field coil and the compensation magnetic field coil, and the current density is i0=NI / [(r2-r1)(z2-z1)], a first excitation magnetic field is generated. and the second excitation magnetic field The object under test will induce eddy currents to generate an induced magnetic field ΔB, where r1, r2, z1, and z2 are the inner diameter, outer diameter, axial starting position, and axial ending position of the excitation magnetic field coil, respectively.

[0055] Since the excitation magnetic field coil and the compensation magnetic field coil are symmetrical about the point P where the magnetic sensor is located, when excitation signals of the same magnitude and opposite directions are applied to the excitation magnetic field coil and the compensation magnetic field coil, the first excitation magnetic field on the magnetic sensor at point P and the second excitation magnetic field The same magnitude and opposite direction, the total excitation magnetic field B (s) The component in the vertical Z direction is zero. The magnetic sensor at point P is affected only by the induced magnetic field ΔB generated by the salt water being measured. Compared to a single excitation coil, the magnetic sensor is affected by both the excitation and induced magnetic fields. However, the magnitude of the induced magnetic field is often much smaller than the excitation field, making it difficult to directly detect changes in the induced magnetic field through the indirect magnetic field.

[0056] For example, a first excitation magnetic field is generated at any point (r, Z) between the salt water to be tested and the excitation magnetic field coil. The second excitation magnetic field generated at any point (r, Z) between the salt water to be measured and the compensation magnetic field coil The first excitation magnetic field and the second excitation magnetic field Superposition is performed to obtain the total excitation magnetic field B (s) (r, Z), where the total excitation magnetic field B (s) (r,Z) is the vertical Z component Expressed as:

[0057]

[0058] in, The first excitation magnetic field The component in the Z direction, The second excitation magnetic field The component in the Z direction. μ0 is the vacuum permeability, i0 is the excitation current density, J0 represents the 0th order Bessel function, a i is the first-order Bessel function J1(a i R), r1 and r2 are the inner and outer diameters of the excitation coil, 2c is the distance between the excitation coils, d is the height of the brine to be measured, and R is the radius of the brine to be measured. The component of the excitation magnetic field in the Z direction at the center point O(0,0) on the upper surface of the brine is

[0059] In one embodiment of the present application, the excitation magnetic field coil generates a first induced magnetic field at the magnetic sensor; the compensation magnetic field coil generates a second induced magnetic field at the magnetic sensor; the first induced magnetic field and the second induced magnetic field are superimposed to generate the induced magnetic field.

[0060] In one embodiment of the present application, the parameters of the induced magnetic field are also used to obtain the phase difference between the induced magnetic field at the magnetic sensor and the excitation magnetic field at the surface center point of the object to be measured close to the side of the magnetic sensor, and / or to obtain the dielectric constant and / or conductivity of the object to be measured.

[0061] For example, the first induced magnetic field ΔB1 induced by the excitation magnetic field coil at the point P where the magnetic sensor is located, the second induced magnetic field ΔB2 induced by the compensation magnetic field coil at the point P where the magnetic sensor is located, the induced magnetic field ΔB is obtained by superimposing the first induced magnetic field and the second induced magnetic field, and the component ΔB of the induced magnetic field ΔB in the Z direction is z Expressed as:

[0062] ΔB z (0,z0)=ΔB z1 (0,z0)+ΔB z2 (0,z0)

[0063]

[0064]

[0065] in, ΔB z1 is the component of the induced magnetic field ΔB1 in the Z direction, ΔB z2 is the component of the induced magnetic field ΔB2 in the Z direction. μ0 is the vacuum magnetic permeability, i0 is the excitation current density, J0 represents the 0th order Bessel function, a i is the first-order Bessel function J1(a i R)=0, eigenvalue of the i-th positive solution, α0=a i , α1=(a2i+jωμ1σ1) 1 / 2 , α2=(a2i+jωμ2σ2) 1 / 2 , d is the thickness of the brine to be measured, σ1 is the conductivity, σ2 is the conductivity of air, μ1 and μ2 are the magnetic permeabilities, r1 and r2 are the inner and outer diameters of the excitation coil, 2c is the distance between the excitation coils, h is the height of the brine to be measured, and R is the radius of the brine to be measured.

[0066] Since the induced magnetic field ΔB at point P is much smaller than the excitation magnetic field B at the center point O on the upper surface of the salt water to be measured, (s) , and the imaginary part of the induced magnetic field ΔB is much larger than the real part, so the phase difference between the induced magnetic field and the excitation magnetic field is expressed as:

[0067]

[0068] Among them, the real part Re(ΔB of the induced magnetic field ΔB z ) represents the dielectric constant of the salt water to be measured, and the imaginary part of the induced magnetic field Im(ΔB z ) represents the conductivity of the salt water to be tested, represents the component of the excitation magnetic field in the z direction.

[0069] For low-conductivity objects, the imaginary part of the induced magnetic field ΔB dominates, so the phase difference can also be expressed as:

[0070]

[0071] In one embodiment of the present application, the induced magnetic field and the phase difference between the induced magnetic field and the excitation magnetic field vary linearly with the thickness of the object to be measured and the conductivity of the object to be measured.

[0072] In some embodiments, the process of obtaining the induced magnetic field and the phase difference change includes:

[0073] S100, dual excitation coils are coaxially arranged above the cylindrical saline sample.

[0074] S101, an alternating current of a specific frequency and amplitude is passed through the dual excitation coils, and the excitation magnetic field at the center point of the surface of the salt water sample to be tested is obtained under different spacing conditions by controlling the frequency and amplitude of the current.

[0075] S102: Analyze the changing relationship between the excitation magnetic field and the coil spacing to obtain the optimal coil spacing.

[0076] S103 , based on different frequency conditions, measure and obtain the induced magnetic field at the center point O(0,0) on the upper surface of the salt water, and the phase difference between the induced magnetic field and the excitation magnetic field.

[0077] For example, the conductivity of the brine to be measured is 2.5S / m, the radius R is 75mm, the thickness d is 10mm, the number of turns N of the excitation coil and the compensation magnetic field are both 10, the inner diameter r1 is 37mm, the outer diameter r2 is 37.5mm, the height z between the bottom of the excitation coil and the brine is, and the spacing between the excitation coil and the compensation coil is 2c. If the amplitude of the first excitation current is 80mA, the frequency f=ω / 2π is 30MHz, the height z between the excitation coil and the brine is kept at 10mm, and the distance c is increased from 0mm to 40mm, the excitation magnetic field at the center of the upper surface of the brine at point O(0,0) is Numerical calculations were performed to obtain the distance c between the excitation coil and the compensation coil and the excitation magnetic field at the origin O (center of the upper surface of the salt water). Then the frequency f=ω / 2π is set to 15MHz, 20MHz, 25MHz and 30MHz in sequence, and the induced magnetic field ΔB at point P(0,z0) is z Numerical calculations are performed to obtain the induced magnetic field ΔB at point P(0,z0) when the brine conductivity is 2.5S / m. z Phase difference The changing relationship when the excitation frequency is 15MHz, 20MHz, 25MHz, and 30MHz. Due to the excitation magnetic field acting on point O by the excitation coil II The compensation coil acts on the excitation magnetic field at point O. As the distance c increases, it decreases, so that the excitation magnetic field at point O After gradually increasing, it tends to be stable, and the phase difference As c increases, it decreases, so the induced magnetic field ΔB z The distance c when the maximum value is reached is taken as the optimal coil spacing, and the optimal coil spacing is 10 mm.

[0078] In some embodiments, the process of obtaining the induced magnetic field and the phase difference change includes:

[0079] S200, dual excitation coils are coaxially arranged above the cylindrical saline sample.

[0080] S201 , passing an alternating current of a specific frequency and amplitude through the dual excitation coils, and measuring the excitation magnetic field at the center point of the upper surface of the salt water sample under different lift-off heights, where the lift-off height is represented by the height of the excitation coils.

[0081] S203 , obtaining an optimal lift-off height based on a relationship between the excitation magnetic field and the lift-off height.

[0082] S204 , based on different frequency conditions, measuring and obtaining the induced magnetic field at a specific position and the phase difference between the induced magnetic field and the excitation magnetic field.

[0083] For example, the number of turns N of the excitation coil and the compensation magnetic field is 10, the inner diameter r1 is 37 mm, the outer diameter r2 is 37.5 mm, the brine radius R is 75 mm, the thickness d is 10 mm, the brine conductivity is set to 2.5 S / m, the excitation current amplitude flowing into the compensation coil is set to 80 mA, the frequency is 30 MHz, the distance c is fixed to 10 mm, the height z (lift-off height) of the excitation line is changed from 6 mm to 20 mm, and the excitation magnetic field size at the center point O (0, 0) on the upper surface of the brine is Numerical calculations were performed to obtain the relationship between the height of the excitation coil and the excitation magnetic field at the origin O (the center of the upper surface of the salt water). When the height z is 12 mm, the excitation magnetic field at point O reaches its maximum. Subsequently, the excitation current flowing into the compensation coil is kept at 80 mA, and the frequency f = ω / 2π is set to 15 MHz, 20 MHz, 25 MHz, and 30 MHz in sequence. By increasing z from 6 mm to 30 mm, the induced magnetic field ΔB at point P (r0, z0) is z Numerical calculations are performed to obtain the induced magnetic field ΔB at point P(0,z0) when the brine conductivity is 2.5S / m. z Phase difference The relationship between the excitation frequencies is shown as follows: 15MHz, 20MHz, 25MHz, and 30MHz. Due to the inherent error of the mechanical device that fixes the magnetic sensor and the weak vibration of the MIT system itself, the height z of the excitation line from the salt water will inevitably have an error of 0.1% or even 1%. When the height z = 5mm, a change of 1mm in the height z will result in an induced magnetic field ΔB z Producing an error of 0.01578μT, the phase difference Produces an error of 0.0042°; when the height z = 12mm and the height z changes by 1mm, the induced magnetic field ΔB z The error generated is only 0.00888μT, and the phase difference The resulting error is 0.00152°. Therefore, the optimal lift-off height is selected as 12mm.

[0084] In some embodiments, the thickness change of the salt water to be measured is inverted by measuring the induced magnetic field change at a specific position and the phase difference between the induced magnetic field and the excitation magnetic field, which is specifically expressed as follows:

[0085] S300, dual excitation coils are coaxially arranged above the cylindrical saline sample.

[0086] S301, based on the optimal coil spacing and excitation current amplitude of the excitation coil, measuring and obtaining the induced magnetic field at a specific position under different salt water thickness conditions, and the phase difference between the induced magnetic field and the excitation magnetic field.

[0087] S302, obtaining the relationship between the induced magnetic field and the phase difference and the thickness of the salt water.

[0088] S303 , maintaining the excitation current amplitude and frequency unchanged, and changing the conductivity of the salt water to be measured to obtain the induced magnetic field and phase difference at a specific position.

[0089] S304: Obtain thickness change of the salt water to be measured according to the induced magnetic field and the phase difference.

[0090] For example, the number of turns N of the excitation coil and the compensation magnetic field is 10, the inner diameter r1 is 37 mm, the outer diameter r2 is 37.5 mm, the brine radius R is 75 mm, the conductivity is constant at 2.5 S / m, the brine thickness d changes from 0 mm to 10 mm, and the distance z between the bottom of the excitation line and the brine is always kept at 12 mm. The amplitude of the excitation current flowing into the compensation coil is 80 mA, and the frequency f = ω / 2π is set to 15 MHz, 20 MHz, 25 MHz, and 30 MHz, respectively. The radial coordinate r of point P is 0 mm, and the longitudinal coordinate z is 27 mm. This is to obtain the induced magnetic field ΔB at point P (0, z0) when the brine conductivity is 2.5 S / m and the excitation frequencies are 15 MHz, 20 MHz, 25 MHz, and 30 MHz, respectively. z Phase difference The relationship between the excitation current amplitude and the brine thickness d is then maintained at 80 mA, the excitation frequency f is 30 MHz, the radial coordinate r of point P is 0 mm, the longitudinal coordinate z is 40.5 mm, the brine conductivity is changed to 1 S / m, 1.5 S / m, 2 S / m and 2.5 S / m, and the brine thickness d is changed from 0 mm to 10 mm to obtain the induced magnetic field ΔB at point P(0,z0) when the excitation frequency is 30 MHz and the brine conductivity is 1 S / m, 1.5 S / m, 2 S / m and 2.5 S / m. z Phase difference Relationship with brine thickness d.

[0091] In some embodiments, the change in conductivity of the salt water to be measured is inverted by measuring the change in the induced magnetic field at a specific position and the phase difference between the induced magnetic field and the excitation magnetic field, which is specifically manifested as:

[0092] S400, dual excitation coils are coaxially arranged above the cylindrical saline sample.

[0093] S401 , keeping the thickness of the salt water to be measured unchanged, and obtaining the induced magnetic field and phase difference at a specific position based on different excitation frequency conditions.

[0094] S402, obtaining the relationship between the induced magnetic field and the phase difference and the conductivity of the salt water.

[0095] S403 , maintaining the excitation current frequency unchanged, and measuring the induced magnetic field and phase difference at a specific position after changing the thickness of the salt water to be measured.

[0096] S404: Obtain the change in conductivity of the salt water to be measured according to the induced magnetic field and the phase difference.

[0097] For example, the saline thickness d is fixed to 10mm, and when the excitation frequencies f are 15MHz, 20MHz, 25MHz and 30MHz respectively and the saline conductivity is 0.1S / m-2.5S / m respectively, the induced magnetic field ΔB at the position point P where the magnetic sensor is located isz and phase difference Calculations are performed to obtain the induced magnetic field ΔB at point P(0,z0) when the salt water thickness d is 10 mm and the excitation frequencies are 15 MHz, 20 MHz, 25 MHz, and 30 MHz respectively. z Phase difference Then the excitation current I frequency f is fixed at 30MHz, and the induced magnetic field ΔBz and phase difference at point P are calculated when the salt water thickness is 2mm, 4mm, 6mm, 8mm and 10mm respectively. The analysis is carried out to obtain the induced magnetic field ΔB at point P(0,z0) when the excitation frequency is 30MHz and the brine thickness is 2mm, 4mm, 6mm, 8mm, and 10mm respectively. z Phase difference With the change of conductivity. According to the magnetic field ΔB induced at point P(0,z0) z Phase difference As the conductivity changes, the induced magnetic field ΔB at different excitation frequencies z It has a good correlation with the conductivity of the measured brine. At the same time, the greater the excitation frequency and the thickness of the brine, the greater the induced magnetic field ΔB z Phase difference The bigger.

[0098] In one embodiment of the present application, the magnetic induction tomography apparatus 1 further includes a signal processing module 15, which is configured to extract parameters of the induced magnetic field, which are used for magnetic induction tomography. The signal processing module may be a spectrum analyzer.

[0099] In one embodiment of the present application, the induced magnetic field detection device includes a function signal generator, a dual excitation coil, a magnetic sensor, a position control device 17, and a signal processing module 15. The signal processing module 15 can be a spectrum analyzer. The magnetic sensor 14 includes: a magnetoelectric sensing unit 141 and a charge amplifier 142. The magnetoelectric sensing unit is fixed on the position control device and fixed on the PCB circuit board. The position control device 17 is used to adjust the position of the magnetoelectric sensing unit. The charge amplifier 142 is connected to the spectrum analyzer, and the spectrum analyzer is used to monitor the signal output by the charge amplifier 142, thereby monitoring the output signal of the magnetic sensor. The charge amplifier 142 amplifies the weak charge signal output by the magnetoelectric sensing unit and converts it into a voltage signal. For the magnetic induction detection process based on the magnetic sensor, please refer to Figure 3 .

[0100] For example, the solution concentration of the test object is obtained according to the mass of sodium chloride crystals and deionized water, wherein the solution concentration formula of the salt water to be tested can be expressed as:

[0101]

[0102] Among them, m NaC1 is the mass of sodium chloride crystals, is the mass of deionized water, and σ is the conductivity of the brine solution.

[0103] In one embodiment of the present application, the magnetoelectric sensing unit includes metallic glass and lithium niobate.

[0104] Furthermore, the magnetoelectric sensing unit also includes a flexible electrode.

[0105] For example, see Figure 4 The preparation process of the magnetoelectric sensing unit includes: fixing two flexible electrodes to the upper and lower surfaces of a lithium niobate single crystal with epoxy glue, and fixing metallic glass as a magnetostrictive layer to the upper and lower surfaces of the solidified lithium niobate or flexible electrode, and connecting copper wires to the flexible electrodes to realize the signal output of the magnetoelectric sensing unit.

[0106] Exemplarily, the performance of the magnetic sensor is tested, and the testing process includes:

[0107] S500: Provide an excitation signal to the excitation coil via a function signal generator to generate a uniform test magnetic field.

[0108] S501, measuring the voltage signal output by the charge amplifier using a spectrum analyzer.

[0109] S502: Obtain a magnetic field voltage coefficient based on the voltage signal and the test magnetic field, wherein the magnetic field voltage coefficient is a ratio of the amplitude of the voltage signal to the amplitude of the test magnetic field.

[0110] S503: Changing the amplitude of the output signal of the function signal generator based on the original excitation signal to reduce the test magnetic field.

[0111] In step S504, the amplitude of the output voltage signal after the reduced test magnetic field is measured using a spectrum analyzer to obtain a corresponding relationship between the amplitude and the test magnetic field. Experiments have shown that as the input signal amplitude decreases, the output signal of the magnetic sensor decreases linearly and eventually stabilizes.

[0112] S505 , stopping providing the excitation signal to the excitation coil, and obtaining the output voltage noise of the magnetic sensor using a spectrum analyzer in the absence of an external excitation magnetic field.

[0113] S506: Obtain an equivalent magnetic noise of the sensor based on the output voltage noise and the magnetic field voltage sensing coefficient, wherein the equivalent magnetic noise is a ratio of the output voltage noise to the magnetic field voltage sensing coefficient.

[0114] For example, the output stability of the low conductivity detection module under different excitation magnetic fields is tested, and the testing process includes:

[0115] S600 , the excitation magnetic field coil and the compensation magnetic field coil generate an excitation magnetic field at the coordinate origin O through a function signal generator.

[0116] S601 , in the absence of salt water to be tested, placing a magnetic sensor at the center of the excitation magnetic field coil and the compensation magnetic field coil, and obtaining the output voltage of the magnetic sensor every minute.

[0117] S602 , obtaining a phase accuracy corresponding to an output variation range based on the output voltage of the magnetic sensor at different frequencies.

[0118] Through the above test process, we know that the phase accuracy can reach (6×10 -5 )°.

[0119] For example, the relationship between the induced magnetic field signal detected by the magnetic sensor and the salt water thickness and salt water conductivity is tested, and the testing process includes:

[0120] S700, gradually increasing the thickness of the configured salt water to be tested.

[0121] S701: Use a position control device to adjust the distance between the bottom of the excitation coil and the surface of the brine to be measured to maintain a fixed height.

[0122] S702, applying excitation signals of different excitation frequencies to the excitation coil through a function signal generator, recording the output voltage of the charge amplifier, and obtaining the relationship between the induced magnetic field and the phase difference between the induced magnetic field and the excitation magnetic field and the thickness of the salt water to be measured.

[0123] S703, maintaining the excitation signal at a fixed frequency, recording the output voltage of the charge amplifier under different conductivity and different salt water thicknesses, and obtaining the relationship between the induced magnetic field and the thickness of the salt water to be measured, as well as the relationship between the phase difference between the induced magnetic field and the excitation magnetic field and the thickness of the salt water to be measured.

[0124] Through the above test process, it is known that under different excitation frequencies and different conductivity brine conditions, the induced magnetic field and phase difference increase linearly with the thickness of the brine. When the excitation frequency and conductivity are larger, the induced magnetic field changes more obviously.

[0125] For example, the relationship between the induced magnetic field signal detected by the magnetic sensor and the conductivity of the salt water is tested, and the testing process includes:

[0126] In S800, a fixed thickness of salt water with varying conductivities is added to the container and the excitation magnetic field is obtained at different excitation frequencies. A position control device maintains the bottom of the excitation coil at a fixed height above the salt water surface. A spectrum analyzer measures the output voltage of the magnetic sensor and determines how the induced magnetic field and phase difference vary with conductivity.

[0127] In step S801, salt water of varying thicknesses is added to the container to obtain salt water of varying conductivities. The position control device maintains the bottom of the excitation coil at a fixed height relative to the salt water surface. A spectrum analyzer is used to measure the output voltage of the magnetic sensor and obtain the relationship between the induced magnetic field and phase difference as the conductivity changes.

[0128] Through the above test process, it is known that as the conductivity increases, under the conditions of different excitation magnetic field frequencies and different brine thicknesses, the induced magnetic field increases linearly with the increase of the conductivity of the brine to be tested.

[0129] In summary, this application uses dual excitation coils to compensate for the excitation magnetic field of the compensating magnetic field coil, thereby reducing the influence of the combined magnetic field on the induced magnetic field of the object to be measured, and achieving direct measurement of the induced magnetic field and the phase difference of the induced magnetic field relative to the excitation magnetic field. This overcomes the current problem of low magnetic field detection sensitivity and difficulty in directly measuring the induced magnetic field when using detection coils as sensing units in magnetic induction tomography systems, thereby improving imaging accuracy. In addition, the low-conductivity detection module based on the magnetic sensor in this application has a higher operating bandwidth while reducing phase noise, thereby improving the quality of magnetic induction tomography.

[0130] The present application also provides a dual excitation coil type induction magnetic field detection method. Figure 5 , the induced magnetic field detection method includes:

[0131] The first excitation magnetic field and the second excitation magnetic field are generated by the excitation magnetic field coil and the compensation magnetic field coil, and the object to be measured generates an induced magnetic field under the action of the first excitation magnetic field and the second excitation magnetic field;

[0132] The component of the induced magnetic field in the Z direction is detected by the magnetic sensor.

[0133] The scope of protection of the induced magnetic field detection method described in the embodiments of this application is not limited to the order of execution of the steps listed in this embodiment. Any solution implemented by adding, subtracting, or replacing steps in the prior art based on the principles of this application is included in the scope of protection of this application. The device for implementing the induced magnetic field detection method described in this application includes but is not limited to the structure of the induced magnetic field detection device listed in this embodiment. Any structural deformation and replacement of the prior art based on the principles of this application is included in the scope of protection of this application.

[0134] The present application also provides an embodiment of a dual-excitation coil induction magnetic field detection system, comprising the aforementioned dual-excitation coil induction magnetic field detection device and an imaging module. The dual-excitation coil induction magnetic field detection device acquires the induction magnetic field signal generated by the object to be detected and converts it into an electrical signal. The electrical signal is transmitted to the imaging module via a signal transmission channel. The imaging module processes the electrical signal using an imaging algorithm to generate a magnetic induction image. In the several embodiments provided in this application, it should be understood that the disclosed systems, devices, or methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of modules / units is merely a logical functional division. In actual implementation, other division methods may be used, such as multiple modules or units can be combined or integrated into another system, or some features can be ignored or not implemented. In addition, the coupling or direct coupling or communication connection shown or discussed can be through some interface, indirect coupling or communication connection of devices, modules, or units, and can be electrical, mechanical, or other forms.

[0135] The modules / units described as separate components may or may not be physically separate, and the components displayed as modules / units may or may not be physical modules, that is, they may be located in one place or distributed across multiple network elements. Some or all of the modules / units may be selected according to actual needs to achieve the purpose of the embodiments of the present application. For example, the functional modules / units in the various embodiments of the present application may be integrated into a processing module, or each module / unit may exist physically separately, or two or more modules / units may be integrated into a single module / unit.

[0136] Those skilled in the art should further appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the above description has generally described the composition and steps of each example according to function. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0137] An embodiment of the present application may also provide an electronic device. Figure 6 The diagram shows the structure of the electronic device 2 in one embodiment of the present application. Figure 6 As shown, in this embodiment, the electronic device 2 includes a memory 21 and a processor 22 .

[0138] The memory 21 is used to store computer programs. In some possible implementations, the memory 21 may include various media capable of storing program codes, such as ROM, RAM, a magnetic disk, a USB flash drive, a memory card, or an optical disk.

[0139] In the embodiment of the present application, the memory 21 may include a computer system readable medium in the form of a volatile memory, such as RAM and / or cache memory. The electronic device 2 may further include other removable / non-removable, volatile / non-volatile computer system storage media. The memory 21 may include at least one program product having a set (e.g., at least one) of program modules configured to perform the functions of the various embodiments of the present application.

[0140] The processor 22 is connected to the memory 21 and is used to execute the computer program stored in the memory 21 so as to enable the electronic device 2 to perform the induced magnetic field detection method.

[0141] Exemplarily, the processor 22 may be a general-purpose processor, including a central processing unit (CPU), a network processor (NP), etc. In other embodiments, the processor 22 may also be a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components.

[0142] The descriptions of the processes or structures corresponding to the above figures have different emphases. For parts that are not described in detail in a certain process or structure, please refer to the relevant descriptions of other processes or structures.

[0143] The above embodiments are merely illustrative of the principles and effects of this application and are not intended to limit this application. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of this application. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical concepts disclosed in this application shall be covered by the claims of this application.

Claims

1. A dual excitation coil induction magnetic field detection device, characterized in that: The induced magnetic field detection device includes: an excitation current source, a magnetic sensor, an excitation magnetic field coil and a compensation magnetic field coil; The excitation magnetic field coil and the compensation magnetic field coil are symmetrical about the magnetic sensor; the excitation current source is used to excite the excitation magnetic field coil to generate a first excitation magnetic field, and is used to excite the compensation magnetic field coil to generate a second excitation magnetic field; at the position of the magnetic sensor, the first excitation magnetic field and the second excitation magnetic field are of the same magnitude and opposite directions in the Z direction; the object to be measured generates an induced magnetic field under the action of the first excitation magnetic field and the second excitation magnetic field; the magnetic sensor is used to detect the component of the induced magnetic field in the Z direction.

2. The dual excitation coil type induction magnetic field detection device according to claim 1, characterized in that: The induced magnetic field detection device further includes a signal processing module, which is used to extract parameters of the induced magnetic field, and the parameters of the induced magnetic field are used for magnetic induction tomography.

3. The dual-excitation coil induction magnetic field detection device according to claim 2, characterized in that: The parameters of the induced magnetic field are also used to obtain the phase difference between the induced magnetic field at the magnetic sensor and the excitation magnetic field at the center point of the surface of the object to be measured on a side close to the magnetic sensor, and / or to obtain the dielectric constant and / or conductivity of the object to be measured.

4. The dual-excitation coil induction magnetic field detection device according to claim 2, characterized in that: The magnetic sensor includes: a magnetoelectric sensing unit and a charge amplifier; the magnetoelectric sensing unit is fixed on a position control device, and the charge amplifier is connected to the signal processing module; the position control device is used to adjust the position of the magnetoelectric sensing unit.

5. The dual-excitation coil induction magnetic field detection device according to claim 4, characterized in that: The magnetoelectric sensing unit includes metallic glass and lithium niobate.

6. The dual-excitation coil induction magnetic field detection device according to claim 1, characterized in that: The excitation magnetic field coil and the compensation magnetic field coil have the same size and the same number of turns.

7. The dual-excitation coil induction magnetic field detection device according to claim 1, characterized in that: The first excitation current flowing into the excitation magnetic field coil and the second excitation current flowing into the compensation magnetic field coil are equal in magnitude and opposite in direction.

8. The dual-excitation coil induction magnetic field detection device according to claim 1, characterized in that: The excitation magnetic field coil and the compensation magnetic field coil are parallel to each other, and the excitation magnetic field coil and the compensation magnetic field coil are coaxially placed directly above the object to be measured.

9. A dual excitation coil induction magnetic field detection method, characterized in that: The dual-excitation coil induction magnetic field detection device applied to any one of claims 1 to 8, wherein the induction magnetic field detection method comprises: The first excitation magnetic field and the second excitation magnetic field are generated by the excitation magnetic field coil and the compensation magnetic field coil, and the object to be measured generates an induced magnetic field under the action of the first excitation magnetic field and the second excitation magnetic field; The component of the induced magnetic field in the Z direction is detected by the magnetic sensor.

10. A dual excitation coil induction magnetic field detection system, characterized in that: The dual-excitation coil induction magnetic field detection system comprises the dual-excitation coil induction magnetic field detection device according to any one of claims 1 to 8 and an imaging module.

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