Miniaturized broadband inductive magnetic field sensor

Abstract

This application relates to the technical field of geophysical exploration instruments, specifically to a miniaturized broadband inductive magnetic field sensor. The sensor includes a magnetic core, an induction coil, a feedback coil, and a signal processing circuit. Its innovation lies in the following: the magnetic core is a long rod-shaped structure solidified from layers of high-permeability soft magnetic tape, with a length between 580mm and 640mm, a cross-section of a square or equivalent circle with sides of 11mm to 15mm, and an aspect ratio greater than 40; the feedback coil is formed by spirally winding a metal foil strip along the magnetic core, which also constitutes the main shielding layer for suppressing external electric field interference. This invention, by optimizing the magnetic core size and aspect ratio, and combining an integrated design of feedback and shielding functions, achieves significant miniaturization and weight reduction of the sensor while ensuring operating bandwidth and low noise performance, greatly improving the portability and deployment efficiency of field exploration.

Description

Technical Field

[0001] This application relates to the technical field of geophysical exploration instruments, specifically to a miniaturized broadband inductive magnetic field sensor. Background Technology

[0002] Inductive magnetic field sensors are magnetic field measurement devices based on Faraday's law of electromagnetic induction and are widely used in geophysical exploration methods such as magnetotelluric sounding. To achieve sufficiently high sensitivity and low noise, traditional inductive magnetic field sensors typically employ a magnetic core with high initial permeability and a large aspect ratio, wound with a large number of coil turns. This results in sensors that are bulky and heavy (often exceeding 1 meter in length and weighing over 5 kilograms). While this structure ensures electrical performance, it severely limits the efficiency of deployment, ease of transport, and operational flexibility in field exploration, especially in complex terrain areas.

[0003] While existing technologies, such as magnetic flux negative feedback, can broaden the operating bandwidth of sensors and stabilize their response, significant shortcomings remain in achieving overall miniaturization and weight reduction. Specifically, this manifests in several ways: difficulty in reducing the core size to maintain performance; the addition of an independent metal shielding cylinder to block external interference increases volume and weight; and complex circuit design. Therefore, developing an inductive magnetic field sensor that significantly reduces size and weight while maintaining core performance characteristics of wide bandwidth, high sensitivity, and low noise has become a pressing technical challenge in this field. Summary of the Invention

[0004] The present invention aims to overcome the above-mentioned defects of the prior art and provide a miniaturized broadband inductive magnetic field sensor.

[0005] The core concept of this invention is to achieve an optimized balance of electrical performance under strict physical constraints by using a high-performance magnetic core with a specific size and aspect ratio, combined with an integrated design of feedback coil and electromagnetic shielding layer, ultimately achieving a unity of miniaturization, lightweight and high performance.

[0006] This application provides a geophysical exploration instrument, including: a magnetic core, an induction coil wound on the magnetic core, a feedback coil, and a low-noise signal processing circuit electrically connected to the induction coil. The magnetic core is a long rod-shaped structure formed by laminating and curing high-permeability soft magnetic tape. The length of the magnetic core is 580 mm to 640 mm, and the cross-section of the magnetic core is a square or equivalent circle with a side length of 11 mm to 15 mm.

[0007] The feedback coil is formed by spirally winding a metal foil strip along the length of the magnetic core. The metal foil strip also forms the main shielding layer in the sensor to suppress external electric field interference. The feedback coil is connected to the output terminal of the low-noise signal processing circuit and the induction coil, respectively.

[0008] Optionally, the high permeability soft magnetic tape is a cobalt-based amorphous or nanocrystalline alloy tape, and the magnetic core is subjected to longitudinal magnetic field annealing treatment at 300°C to 380°C, with an initial permeability of not less than 50,000.

[0009] Optionally, the magnetic core has a length of 610mm ± 0.2mm and a cross-section of a square with a side length of 13mm ± 0.2mm.

[0010] Optionally, the fill factor of the magnetic core is greater than 70%, and the interlayer of the flexible magnetic tape is coated with a high-temperature insulating oxide coating.

[0011] Optionally, the induction coil is wound on a frame using a quasi-random winding method or a segmented winding method. The frame is fitted outside the magnetic core and divides the induction coil into multiple segments.

[0012] Optionally, the frame includes a plurality of parallel partitions that divide the induction coil into 14 to 18 segments, with a spacing of 20 mm to 25 mm between adjacent partitions.

[0013] Optionally, the metal foil strip is copper foil with a width of 15mm to 25mm, and the feedback coil has 30 to 40 turns.

[0014] Optionally, a calibration coil is also wound outside the feedback coil.

[0015] Optionally, the low-noise signal processing circuit includes a preamplifier stage and an amplification and filtering stage;

[0016] The preamplifier stage includes a differential amplifier circuit composed of super-matched differential pairs and a constant current source circuit.

[0017] The amplification and filtering stage is electrically connected to the preamplifier stage and includes an operational amplifier and a T-type filter network composed of resistors and capacitors.

[0018] Optionally, the sensor operates in a frequency range of 0.1Hz to 10kHz, has a noise floor of less than 10 fT / √Hz at 1kHz, an overall weight of less than 4kg, and a maximum outer diameter of less than 65mm.

[0019] This application discloses a miniaturized broadband inductive magnetic field sensor. By optimizing the core size within a specific range (580-640mm in length, 11-15mm in cross-sectional side length), the size of the core components is significantly reduced while ensuring sufficient magnetic focusing ability and operational linearity. In particular, the use of metal foil strips (such as copper foil) as both the feedback coil and the main shielding layer eliminates the need for traditional, separate, heavy metal shielding cylinders, further reducing the sensor's weight and radial dimensions. This results in a compact design with an overall weight of less than 4kg and an outer diameter of less than 65mm, greatly improving portability in the field. The magnetic core, treated with specific components (such as cobalt-based amorphous materials) and a specific process (longitudinal annealing at 300-380℃), provides high and stable effective permeability. By combining optimized coil winding methods (quasi-random or segmented winding) and low-noise circuit design, the sensor achieves a flat, high-sensitivity response and extremely low noise floor (less than 10 fT / √Hz at 1kHz) across a wide frequency band of 0.1Hz-10kHz, fully meeting the requirements of high-precision AMT / CSAMT exploration. After optimized magnetic field annealing, the effective permeability of the magnetic core is less affected by temperature and time drift of the material's intrinsic parameters, improving the sensor's long-term stability. The integrated shielding design also enhances its resistance to external interference. The specific circuit architecture eliminates the need for complex chopper stabilization techniques within the target frequency band, improving system reliability. Attached Figure Description

[0020] The above and other objects, features, and advantages of this application will become more apparent from the more detailed description of the embodiments of this application in conjunction with the accompanying drawings. The drawings are provided to further illustrate the embodiments of this application and form part of the specification. They are used together with the embodiments of this application to explain this application and do not constitute a limitation thereof. In the drawings, the same reference numerals generally represent the same components or steps.

[0021] Figure 1 This is a schematic diagram illustrating the relationship between effective permeability, aspect ratio, and initial permeability according to an embodiment of this application;

[0022] Figure 2 This is a magnetic core diagram of an inductive magnetic field sensor provided in one embodiment of this application;

[0023] Figure 3 This is a schematic diagram of a high-frequency circuit for an inductive magnetic field sensor provided in one embodiment of this application;

[0024] Figure 4 This is a magnetic core sample test - hysteresis loop provided in one embodiment of this application;

[0025] Figure 5 This is a schematic diagram of sensor design dimensions provided in one embodiment of this application;

[0026] Figure 6 This is a schematic diagram of a skeleton partition provided in one embodiment of this application;

[0027] Figure 7 This is a schematic diagram of the dimensions of a skeleton partition provided in one embodiment of this application;

[0028] Figure 8 This is a schematic diagram of the sensor main coil skeleton provided in one embodiment of this application;

[0029] Figure 9 This is a schematic diagram of a sensor feedback coil frame provided in one embodiment of this application;

[0030] Figure 10 This is a schematic diagram of the overall structure of a sensor provided in one embodiment of this application;

[0031] Figure 11 This is a schematic cross-sectional view of the overall structure of the sensor provided in one embodiment of this application;

[0032] Figure 12 This is a schematic diagram of the winding direction of the main induction coil provided in one embodiment of this application;

[0033] Figure 13 This is a schematic diagram of the overall structure of the main induction coil provided in one embodiment of this application;

[0034] Figure 14 This is a schematic diagram of the feedback coil of a CSAMT inductive magnetic field sensor provided in one embodiment of this application;

[0035] Figure 15 This is a schematic diagram of the calibration coil of a CSAMT inductive magnetic field sensor provided in one embodiment of this application;

[0036] Figure 16 This is a schematic diagram of the CSAMT sensor circuit provided in one embodiment of this application;

[0037] Figure 17 This is a schematic diagram of a preamplifier circuit provided in one embodiment of this application;

[0038] Figure 18 This is a schematic diagram of a DC path provided in one embodiment of this application;

[0039] Figure 19 This is a schematic diagram of a small-signal equivalent circuit provided in one embodiment of this application;

[0040] Figure 20 This is an amplification and filtering circuit diagram provided in one embodiment of this application. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] The miniaturized broadband inductive magnetic field sensor provided in this application includes a magnetic core, an induction coil wound on the magnetic core, a feedback coil, and a low-noise signal processing circuit electrically connected to the induction coil;

[0043] The magnetic core is a long rod-shaped structure formed by stacking and curing high-permeability soft magnetic tape. The length of the magnetic core is 580mm to 640mm, and the cross-section of the magnetic core is a square or equivalent circle with a side length of 11mm to 15mm.

[0044] The feedback coil is formed by spirally winding a metal foil strip along the length of the magnetic core. The metal foil strip also forms the main shielding layer in the sensor to suppress external electric field interference.

[0045] To achieve a balance between miniaturization and high performance, the key dimensions of the magnetic core were carefully designed: its length was limited to between 580 mm and 640 mm, and its cross-sectional shape was a square with sides of 11 mm to 15 mm, or an equivalent circle with an area comparable to this square. This configuration allows the core to achieve sufficiently high effective permeability and sensitivity within a limited volume.

[0046] More noteworthy is the innovative design of the feedback coil. Instead of being wound with traditional circular cross-section enameled wire, it is formed by spirally winding a strip of metal foil along the length of the magnetic core. This design offers a key advantage: while the metal foil acts as the feedback coil, generating a reverse magnetic field for stable operation, its continuous metal surface naturally forms the main shielding layer of the entire sensor, effectively suppressing interference from external stray electric fields. This design, integrating feedback and electromagnetic shielding functions, eliminates the need for a separate shielding cylinder in traditional solutions, representing a core innovation that significantly reduces sensor weight and radial dimensions.

[0047] In some embodiments, the high permeability soft magnetic tape is a cobalt-based amorphous or nanocrystalline alloy tape, and the magnetic core is subjected to longitudinal magnetic field annealing treatment at 300°C to 380°C, with an initial permeability of not less than 50,000.

[0048] To achieve the necessary high sensitivity and low noise for the sensor within the constraints of miniaturization, the materials and processes for the magnetic core were meticulously selected and optimized. Specifically, the magnetic core uses thin strips of cobalt-based amorphous alloys or cobalt-based nanocrystalline alloys as the base material. These cobalt-based soft magnetic materials are highly favored due to their extremely high initial permeability, extremely low coercivity, and near-zero magnetostriction coefficient. High initial permeability significantly enhances the magnetic core's magnetizing ability, efficiently concentrating weak ambient magnetic fields and directly improving the sensor's sensitivity; low coercivity and low hysteresis loss help reduce noise introduced by the magnetic core itself; and near-zero magnetostriction means the material is extremely insensitive to external stress, which greatly enhances the sensor's mechanical and temperature stability in complex field environments.

[0049] However, the strips fresh off the production line contain internal stress and have disordered magnetic domain arrangement, resulting in magnetic properties far from optimal. Therefore, a crucial longitudinal magnetic field annealing step is indispensable. The laminated core blank is placed in a magnetic field of a specific direction and heat-treated within a precise temperature range of 300°C to 380°C. This temperature window is an optimized range verified through repeated experiments: if the temperature is too low, the internal stress of the material cannot be sufficiently eliminated, and the magnetic domains are difficult to achieve ideal orientation; if the temperature is too high, the material may undergo undesirable crystallization transformations or performance degradation, impairing its soft magnetic properties. Annealing under the action of a longitudinal magnetic field guides the magnetic domains within the material to align orderly along the axial direction (i.e., the length direction) of the core, thereby maximizing its permeability in that direction.

[0050] Through the combination of the aforementioned specific materials and processes, the resulting magnetic core achieves an initial permeability that is consistently at an excellent level of no less than 50,000. This high permeability is the core material basis for ensuring the effective operation of the magnetic core, thereby supporting the sensor's continued superior detection performance even after its size has been reduced. It directly determines the sensor's ability to convert weak magnetic field signals into measurable electrical signals, making it a crucial step in the entire design process from theory to high-performance realization.

[0051] In some embodiments, to achieve the best balance between theoretical calculations and engineering practice, and to provide a stable and reliable core component for the sensor, the machining dimensions of the magnetic core are further precisely defined. The magnetic core has a length of 610 mm ± 0.2 mm and a cross-section of a square with sides of 13 mm ± 0.2 mm.

[0052] This specific set of dimensions (610mm × 13mm × 13mm) represents the optimal design point determined by the inventors after in-depth theoretical modeling, simulation calculations, and multiple rounds of prototype experiments. Within the previously protected wide range (length 580-640mm, cross-sectional side length 11-15mm), it represents an implementation scheme with particularly outstanding performance. Choosing a length of 610mm ensures that the magnetic core provides sufficient axial space to efficiently concentrate magnetic flux while meeting the requirements of a compact overall sensor structure (typically the total length can be controlled to about 800mm). The 13mm × 13mm square cross-section is the result of optimization after comprehensively considering multiple factors: it provides sufficient cross-sectional area to ensure a certain mechanical strength and good heat dissipation; its regular shape facilitates the subsequent precision winding of the coil and the installation of the frame; more importantly, this dimension combined with the 610mm length makes the aspect ratio (length to equivalent diameter ratio) of the magnetic core approximately 50. This ratio falls within the "golden range" that effectively improves the apparent permeability of the magnetic core, significantly reduces sensor noise, and avoids easy magnetic saturation in the geomagnetic field due to excessively high permeability.

[0053] Strict control over dimensional tolerances (±0.2mm) is crucial for ensuring product consistency and performance reliability. This means that the geometry of the magnetic core is highly standardized, ensuring that every sensor produced in batches has highly consistent sensitivity and frequency response characteristics. Therefore, this embodiment of precise dimensions not only serves as a concrete example of achieving the invention's objectives but also represents best practice in balancing manufacturability, superior performance, and cost control.

[0054] In some embodiments, to ensure efficient operation and low loss of the magnetic core across a wide frequency range, further specific requirements are placed on its internal structure and manufacturing process. On one hand, the fill factor of the magnetic core is designed to be greater than 70%. The fill factor refers to the percentage of volume actually occupied by ferromagnetic material (i.e., flexible magnetic tape) within the magnetic core. A high fill factor (>70%) means a very "dense" core structure with a low proportion of internal air gaps or non-magnetic binders. This directly brings two major benefits: First, it significantly increases the effective cross-sectional area of ​​the magnetic core, allowing more ambient magnetic flux to be concentrated and pass through the induction coil, thereby directly improving the sensor's sensitivity; second, a high fill factor enhances the structural integrity of the magnetic core, making its performance more stable under mechanical vibration or temperature changes.

[0055] On the other hand, to achieve a high fill factor while simultaneously suppressing eddy current losses at high frequencies, the layers of the flexible magnetic tape used in the stack are coated with a high-temperature insulating oxide coating. During the fabrication of the magnetic core, each extremely thin sheet of flexible magnetic tape (e.g., approximately 0.02 mm thick) is uniformly coated with an extremely thin but dense insulating material before or during stacking; commonly used materials include magnesium oxide (MgO) or aluminum oxide (Al2O3). This coating plays a crucial role and has the following functions:

[0056] Electrical insulation: It establishes a reliable insulating barrier between adjacent conductive metal strips, breaking down potentially large transverse eddy current loops into countless tiny loops confined within a single layer of strip, thereby minimizing eddy current losses. This is crucial for sensors to maintain low noise at high frequencies of several kilohertz (kHz).

[0057] High temperature resistance: This type of oxide coating can withstand subsequent magnetic field annealing processes at 300°C to 380°C without being damaged or failing, ensuring the durability of insulation performance.

[0058] Maintaining fill factor: The coating is very thin, so it achieves excellent insulation with almost no additional interlayer gap, which helps to achieve the design goal of a high fill factor of more than 70%.

[0059] Therefore, the features of "fill factor greater than 70%" and "interlayer coating with high-temperature insulating oxide coating" are complementary. Together, they solve a core contradiction in magnetic core design: maximizing magnetization through high-fill magnetic materials (enhancing sensitivity) while minimizing high-frequency eddy current losses through excellent interlayer insulation (ensuring high-frequency performance and low noise). This combined design is a crucial technological guarantee for ensuring the miniaturized magnetic core performs excellently across a wide frequency band from 0.1Hz to 10kHz.

[0060] In some embodiments, to achieve excellent electrical characteristics of the induction coil and to facilitate the overall miniaturization of the sensor, its winding method and support structure are specially considered. The induction coil is not directly and tightly wound onto the magnetic core, but rather wound onto a separate frame using a quasi-random winding method or a segmented winding method. This frame is then fitted and fixed outside the magnetic core. That is, the induction coil is wound onto the frame using a quasi-random winding method or a segmented winding method, the frame is fitted outside the magnetic core, and the induction coil is divided into multiple segments.

[0061] This design serves two key purposes. First, it reduces distributed capacitance and optimizes high-frequency response. Traditional tightly wound coils create significant parasitic capacitance between layers and turns. This distributed capacitance, along with the coil's own inductance, forms a parallel resonant circuit, producing a sharp peak at a specific frequency (resonant frequency), severely distorting the sensor's frequency response and potentially causing oscillations. By employing quasi-random winding (where turns are crossed and transposed according to a specific pattern, reducing parallel arrangement) or segmented winding (dividing the entire coil into several groups with gaps between groups or reverse winding), the uniform electric field formed by the capacitance can be significantly disrupted, effectively reducing the overall distributed capacitance. This allows the sensor's resonant frequency to be increased, the operating bandwidth to extend to higher frequencies, and the response within the passband to be flatter.

[0062] Secondly, it provides precise mechanical support and positioning to ensure consistent performance. The skeleton is a pre-fabricated insulating structure (usually made of engineering plastic) with specific slots or partitions. It is precisely fitted around the magnetic core, providing an accurate and stable path for the winding of the enameled wire. More importantly, the skeleton divides the entire winding area of ​​the induction coil into multiple discrete segments. This division not only physically forms the basis for segmented winding but also electrically helps to average the parameters of different parts of the coil, making the key parameters of the final coil, such as inductance, resistance, and distributed capacitance, more stable and controllable, and greatly improving consistency during mass production.

[0063] Therefore, combining the "quasi-random / segmented winding method" with the "segmented frame" is an innovative solution to address the contradiction of compact internal space in miniaturized sensors while demanding extremely high electrical performance. Within a limited physical space, it maximizes the performance of the induction coil, the core transducer component, and is a crucial technical step in ensuring the sensor achieves "wideband" characteristics.

[0064] In some more specific designs, the structure of the frame is further defined to precisely realize the benefits of the aforementioned segmented winding method and to finely control the geometric parameters of the induction coil. Specifically, the frame includes multiple parallel partitions. These partitions are equidistant or arranged according to a specific pattern along the axial direction of the magnetic core, and their core function is to divide the area where the induction coil is to be wound into multiple independent winding slots or segments. In one specific embodiment, the number of partitions is designed to divide the induction coil into 14 to 18 segments.

[0065] This range of 14-18 segments is an optimized choice. Too few segments (less than 14 segments) have limited effect on reducing distributed capacitance and averaging parameters; too many segments (more than 18 segments) significantly increase the complexity of the frame and assembly time, and may reduce the winding window due to the excessive space occupied by the partitions themselves, which is not conducive to obtaining the required inductance. The 14-18 segment design achieves a good balance between effectiveness and complexity.

[0066] Furthermore, the spacing between adjacent partitions is set within the range of 20 to 25 millimeters. This spacing parameter is crucial, as it directly determines the axial length of each segment. A spacing of 20-25 mm means that the length of each segment is controlled within this range, which brings several advantages:

[0067] Optimize electrical parameters: This length helps to keep the distributed capacitance of a single coil segment at a low level, while also facilitating the calculation and acquisition of the total target inductance.

[0068] Ensuring the quality of the winding process: Too small a spacing will make manual or automatic winding operations difficult; within this range, the spacing ensures both sufficient operating space and that the coil is wound tightly and neatly.

[0069] Promotes heat dissipation and mechanical stress relief: The gaps between segments (i.e., the partition area) provide tiny ventilation and heat dissipation channels for the coil, and provide stress buffer space for the enameled wire when the sensor is subjected to temperature changes or slight deformation, thereby improving reliability.

[0070] Therefore, the two related parameters, "14 to 18 segments" and "20 mm to 25 mm spacing," together define an optimized skeleton topology. This is not only the physical carrier for realizing segmented coils with low distributed capacitance, but also a key structural design element ensuring sensor performance consistency, reliability, and manufacturability.

[0071] In some embodiments, to achieve optimal performance and manufacturing feasibility of the feedback coil, and to fully leverage its integrated shielding advantages, specific materials and structural parameters are clearly defined. The metal foil strip is preferably copper foil. Copper possesses excellent conductivity and flexibility, is easily processed into foil strips of the required width, and can achieve reliable electrical connections through welding or crimping, making it an ideal choice in engineering practice.

[0072] The width of the copper foil is set within the range of 15 mm to 25 mm. This width range is determined by comprehensive consideration: if the width is too narrow (e.g., less than 15 mm), more turns are required to obtain the required feedback magnetic field strength, increasing process complexity and coil resistance; if the width is too wide (e.g., more than 25 mm), it is difficult to achieve tight and flat spiral winding on the limited circumference of the magnetic core, and the rigidity of the copper foil itself may cause operational difficulties or generate stress when the sensor is bent. A width of 15 mm to 25 mm ensures sufficient current carrying capacity and effective shielding coverage while ensuring smooth winding process and regular coil formation.

[0073] Meanwhile, the number of turns in the feedback coil is designed to be 30 to 40. This range of turns, along with the copper foil width and core size, determines the key parameters of the feedback coil: inductance and feedback coefficient. In a flux negative feedback system, the feedback coil needs to generate a sufficiently strong reverse magnetic field to effectively counteract the input magnetic field. A number of 30 to 40 turns, combined with the selected copper foil width and core parameters, allows for the calculation of a suitable inductance value that matches the feedback resistor in the circuit. This achieves deep and stable negative feedback within the target frequency band (0.1Hz-10kHz), ensuring the flatness of the sensor's frequency response and an extended operating bandwidth. Too many or too few turns can lead to feedback that is too strong or too weak, affecting system stability and performance.

[0074] Therefore, the combination of the parameters "copper foil width of 15mm to 25mm" and "30 to 40 turns" represents the concrete engineering implementation of the core invention—the integrated feedback / shielding structure with metal foil. These parameters ensure that this innovative design is not only theoretically feasible but can also be implemented in actual products in a stable, reliable, and efficient manner.

[0075] In some embodiments, to further enhance the practicality and long-term reliability of the sensor, after the core feedback coil is wound, an independent functional coil—a calibration coil—is added externally. Specifically, the calibration coil is wound directly outside the metal foil strip that serves as both the feedback coil and the main shielding layer.

[0076] The core purpose of adding a calibration coil is to achieve on-site, in-situ calibration and periodic verification of sensor sensitivity. Its working principle is as follows: the user or detection system can inject a precise current signal of known amplitude and frequency into this independent calibration coil via an external instrument. This current generates a highly controllable calibration magnetic field of known intensity inside the calibration coil. This calibration magnetic field is superimposed on the magnetic field of the measured environment and is sensed by the sensor's magnetic core and induction coil, ultimately generating a corresponding voltage signal at the output. By comparing the injected known current (or known magnetic field) with the sensor's output voltage, the actual sensitivity coefficient of the sensor in the current state can be accurately calculated (the unit is usually V / nT).

[0077] This design solves a common problem in the practical use of traditional inductive sensors: to confirm whether the sensor performance has drifted or to perform accurate measurements, it is often necessary to take the sensor back to the laboratory and test it in a large, sophisticated Helmholtz coil calibration system, a cumbersome process that cannot be performed in the field. The calibration coil integrated into the sensor body is equivalent to having a miniature "magnetic field generator" with known parameters built into it, allowing users to quickly and conveniently perform sensitivity calibration at any deployment location, greatly improving the flexibility of use and the reliability of data quality.

[0078] It is worth noting that the winding of the calibration coil must ensure that the electromagnetic coupling between it and the internal feedback coil and induction coil is fixed and known. It is usually precisely wound with enameled wire with a small number of turns (e.g., a few to tens of turns). Placing it outside the feedback coil avoids interference with the operation of the core feedback loop and utilizes the existing structure as support. This is a clever and practical design extension of the present invention in achieving high integration and multifunctionality.

[0079] In some embodiments, the low-noise signal processing circuit is carefully designed as a two-stage core architecture to achieve extreme amplification and precise conditioning of the weak differential signal output from the induction coil. This circuit mainly includes a pre-amplifier stage and an amplification-filtering stage, which work together to ensure that the sensor has an extremely high signal-to-noise ratio and stable gain over a wide frequency band.

[0080] As the first stage of the entire signal chain, the preamplifier stage directly determines the system's noise floor level. The core of this stage is a differential amplifier circuit composed of super-matched differential transistor pairs. Super-matched differential transistor pairs are pairs of transistors that have undergone special matching processes during manufacturing, resulting in highly consistent characteristic parameters (such as gain and temperature coefficient). The differential amplifier circuit formed by these transistors can amplify the differential signal output from the induction coil with extremely high common-mode rejection ratio (CMRR), while strongly suppressing common-mode noise interference from the power supply, ground, and environment, providing a "clean" signal foundation for subsequent processing. Furthermore, this stage includes a constant current source circuit, which provides an extremely stable quiescent operating current to the differential transistor pairs. The high dynamic impedance of the constant current source ensures that the common-mode rejection capability of the differential amplifier circuit remains excellent under actual operating conditions, and its stable bias also helps reduce DC drift caused by power supply fluctuations or temperature changes, thereby improving the long-term stability of the entire sensor system.

[0081] The amplification and filtering stage, connected after the preamplifier stage, is responsible for providing the main voltage gain and shaping the frequency response. Its core is an operational amplifier, characterized by high input impedance, low output impedance, and low noise. Surrounding this operational amplifier are specific resistors and capacitors, forming a T-type filter network. Compared to a simple RC filter network, the T-type network can provide a steeper roll-off characteristic with the same component values, or use larger resistors (which help reduce thermal noise) and smaller capacitors (potentially smaller and more stable) for the same filtering requirements. Therefore, this T-type network can accurately set the upper cutoff frequency of the sensor, effectively filtering out high-frequency noise and potential RF interference outside the operating frequency band, while working with the preamplifier stage to create a flat and consistent amplitude response throughout the passband.

[0082] Combining these two circuit stages and supplementing them with an appropriate feedback network (connected to the feedback coil) constitutes a complete magnetic flux negative feedback system. This circuit design not only achieves effective amplification of weak nanovolt-level signals, but also systematically suppresses noise introduced by the circuit itself (such as transistor noise and resistor thermal noise) and external interference through specific means such as differential structure, constant current bias, and T-type filtering. This provides the key electronic guarantee for the sensor to achieve a femtosecond (fT / √Hz) equivalent magnetic noise index in a wide frequency range from 0.1Hz to 10kHz.

[0083] In some embodiments, the key performance indicators achieved by the miniaturized broadband inductive magnetic field sensor are specifically quantified, and these indicators are a direct reflection of its inventive value and technological progress.

[0084] First, the sensor operates over a frequency range of 0.1 Hz to 10 kHz. This frequency band fully encompasses the core operating frequencies of both Audio-Tone Magnetotelluric (AMT) and Controlled-Source Audio-Tone Magnetotelluric (CSAMT), enabling it to effectively detect geoelectric structures from shallow to medium depths. The flat response from extremely low frequencies (0.1 Hz) to relatively high frequencies (10 kHz) is the result of the synergistic effect of core design, coil optimization, and circuit negative feedback technology.

[0085] Secondly, a crucial performance characteristic is its extremely low noise level. Specifically, the sensor's noise floor at 1 kHz is less than 10 fT / √Hz (fetates per radian hertz). This value represents the power spectral density of the random magnetic noise generated by the sensor itself in the kilohertz band, which is far lower than the typical geomagnetic field signal strength in this band, ensuring the sensor has extremely high signal resolution and detection sensitivity. This ultra-low noise performance is a direct result of the aforementioned high-stability cobalt-based magnetic core, low-distribution capacitance coil, and ultra-low noise preamplifier circuit.

[0086] Finally, the physical miniaturization and lightweighting of the sensor are defined by two specific parameters: its overall weight is less than 4 kg and its maximum outer diameter is less than 65 mm.

[0087] Weighing less than 4kg: This achievement stems directly from core structural innovations, particularly the integrated feedback / shielding design using metal foil strips, eliminating the need for traditional, separate, heavy metal shielding cylinders. Combined with an optimized magnetic core and compact circuitry, this results in a significant reduction in overall weight.

[0088] Maximum outer diameter less than 65mm: This size limitation is a direct result of the optimization of the magnetic core cross-sectional dimensions (side length 11-15mm) and the integrated compact structural design. It makes the sensor highly portable, facilitating single-person transport and deployment in complex terrain.

[0089] In summary, the three sets of indicators—"wide bandwidth," "low noise," and "small and lightweight"—together define a sensor product with superior performance and ease of field use. These not only validate the success of the technical solution of this invention but also clearly define the advantages of this invention compared to traditional bulky and cumbersome high-performance sensors, concretely embodying the technical effects claimed in this application.

[0090] The following section provides a further explanation of the solution provided in this application, with reference to specific details:

[0091] Typically, the parameter used to measure the performance of magnetic core materials is the relative permeability (or initial permeability). μ rFor inductive magnetic field sensors, since the magnetic core has a demagnetizing field, the parameter for measuring the performance of the magnetic core is the effective permeability. μ app Generally, the core material of inductive magnetic field sensors is a soft magnetic material with high permeability, typically permalloy, amorphous, or nanocrystalline materials. Studies have shown that the effective permeability of a cylindrical magnetic core can be accurately calculated using a formula. When the aspect ratio of the magnetic core is l / d (where l is the length of the magnetic core,) d When the core cross-sectional diameter (i.e., the equivalent diameter) is greater than 10, the effective permeability of the core is approximately:

[0092]

[0093] Demagnetization factor of magnetic core N B It can be simplified to:

[0094]

[0095] The induced voltage of an inductive magnetic field sensor is related to the effective permeability of the magnetic core. μ app The effective permeability of the magnetic core is closely related to its shape and size. μ app Compared with the length-to-diameter ratio l / d and the initial permeability of the core material itself μ r Related. When the aspect ratios of the fixed magnetic core are 10, 20, 50, 100, and 200, Figure 1 The relationship between the effective permeability of the magnetic core and the initial permeability is shown.

[0096] like Figure 1 As shown, for a fixed aspect ratio, the effective permeability of the core material increases with the increase of the initial permeability. However, when the initial permeability is greater than 10000, the effective permeability no longer increases for cores with different aspect ratios, and is determined solely by the aspect ratio. Generally, the initial permeability of the core material is not a constant value; it changes with frequency, temperature, and time. However, when the initial permeability of the core material in an inductive magnetic field sensor is chosen to be greater than 10000, the effective permeability of the core is determined only by the aspect ratio. In this way, the effective permeability of the core no longer changes with frequency, temperature, or time, ensuring the stability of the inductive magnetic field sensor.

[0097] To reduce eddy current effects, the magnetic core of an inductive magnetic field sensor is formed by stacking several long strips of high-permeability material together, ultimately resulting in a rod shape (e.g., Figure 2As shown in the figure, there are air gaps between the core laminations. For the entire rod-shaped core, the percentage of ferromagnetic material in the entire core is the fill factor η.

[0098] Assuming the cross-section of the magnetic core is square with side length *a*, and neglecting leakage flux, the effective cross-sectional area of ​​the magnetic core is the cross-sectional area *S* through which the magnetic flux through the coil passes, expressed as:

[0099]

[0100] After equating it to a cylindrical rod-shaped magnetic core, the equivalent diameter d is:

[0101]

[0102] Then, the effective permeability of the magnetic core can be calculated using the above formula. Theoretically, the larger the aspect ratio, the greater the voltage induced by the sensor coil, and the lower the noise level of the sensor. However, this type of optimization is limited by three factors. First, the length of the magnetic core determines the length of the sensor. For slender magnetic cores, inductive magnetic field sensors can only be made slender. Therefore, when designing inductive magnetic field sensors, the overall length of the sensor limits the length of the magnetic core. Second, due to limitations in magnetic core manufacturing processes, the width of the magnetic core laminations cannot be too small, so the cross-sectional area of ​​the magnetic core cannot be too small either. Third, the magnetic core is made of soft magnetic material. When placed in the Earth's magnetic field, if the aspect ratio is too large and the surface permeability is too high, the magnetic core will be magnetized and saturated by the Earth's magnetic field. The aspect ratio of the magnetic core of an inductive magnetic field sensor is designed to be between 50 and 100, which can concentrate magnetic flux, reduce the sensor noise level, and at the same time ensure that it will not be magnetized and saturated by the Earth's magnetic field, thus operating in the linear segment of the BH curve of the magnetic core material and avoiding nonlinear saturation distortion.

[0103] The induction coil is made of precision enameled wire wound around the outside of the magnetic core, with the magnetic core and coil separated by a core sleeve made of engineering plastic. The induction coil section includes a series of design parameters, which are optimized for different magnetic cores and circuit conditions to obtain an optimal inductive magnetic field sensor. Furthermore, the sensor coil can use a segmented winding method or a quasi-random winding method to reduce distributed capacitance. The feedback coil is wound in the opposite direction to the main coil, uniformly covering the length of the magnetic core.

[0104] In signal processing schemes, inductive magnetic field sensors based on magnetic flux negative feedback structures compensate for the deficiencies of circuit compensation methods. The principle is as follows: the alternating magnetic field being measured generates an induced voltage in the sensor's induction coil. After amplification and filtering, the voltage of the signal is converted into a current through the feedback circuit and applied to the feedback coil, forming a feedback magnetic field opposite to the direction of the measured magnetic field. This forms a closed-loop system for the sensor, improving stability while eliminating the introduction of external electrical noise.

[0105] Since the voltage output of the sensor's induction coil is proportional to the amplitude and frequency of the measured magnetic field, the requirements for the amplifier differ when measuring magnetic field signals in different frequency bands. For high-frequency magnetic field measurements, low-noise amplifier circuits do not require chopping technology, making the circuit relatively simple. This circuit also employs a flux negative feedback structure, the principle of which is as follows... Figure 3 As shown.

[0106] The measured magnetic field is converted into a voltage signal by an induction coil. After amplification and filtering, the resulting voltage is converted into a feedback magnetic field by a feedback circuit. Subtracting this feedback magnetic field from the measured magnetic field yields the net magnetic field, thus forming magnetic flux negative feedback. The amplification factor of the amplifier circuit primarily determines the passband width of the sensor in the high-frequency range, improving the sensor's sensitivity. The filter mainly limits the bandwidth of the amplifier circuit and reduces its noise.

[0107] The magnetic field sensing component is a device that converts the measured electromagnetic signal in the ambient space into a usable output electrical signal. The magnetic field sensing component is the core of a magnetic field sensor.

[0108] The magnetic core is the core component of a magnetic sensor, used to concentrate magnetic flux. The performance of the magnetic core material directly affects the quality of the sensor's output signal. During the project implementation, in order to improve the performance of the magnetic sensor, considering the magnetic and physical properties of various soft magnetic materials, a Co-based alloy was selected as the magnetic core material. This is beneficial for the acquisition of effective signals, and the high-quality measurement results also facilitate subsequent data analysis.

[0109] Based on the performance characteristics of inductive magnetic field sensors, the main selection criteria for magnetic core materials are: low magnetostriction coefficient, high Curie temperature, high effective permeability, high saturation magnetic induction, and low magnetic loss. Typical materials include soft magnetic ferrites, permalloys, amorphous alloys, and nanocrystalline alloys.

[0110] Cobalt-based amorphous ribbons are selected and annealed. After annealing, the initial permeability is not less than 50,000 and the maximum permeability reaches 1,000,000 (not less than 350,000).

[0111] To improve the permeability of magnetic materials, the core material needs to be annealed to eliminate residual stress from machining and to de-disorder the magnetic domains, bringing the material's magnetic properties to their optimal state. Annealing requires a heating furnace, and a thermal demagnetizing furnace is optimal for annealing magnetic materials. For cobalt-based amorphous materials, the annealing effect is related to the difference ΔT between the crystallization temperature and the Curie temperature. To obtain a core with high permeability and low loss, the crystallization temperature must be higher than the Curie temperature, i.e., ΔT > 0; the larger ΔT is, the better the effect. During annealing, the annealing temperature must be lower than the crystallization temperature (generally not exceeding 500℃). Typically, the annealing temperature for high-frequency applications is slightly higher than that for low-frequency applications. To avoid damage during use due to excessive brittleness after annealing, the actual annealing temperature must be adjusted as needed, sacrificing some core performance.

[0112] There are many types of magnetic field annealing, mainly including: longitudinal magnetic field annealing, transverse magnetic field annealing, rotating magnetic field annealing, oblique magnetic field annealing, strong constant magnetic field annealing, and pulsed magnetic field treatment. In short, the purpose of magnetic field annealing is to change the hysteresis loop of a material for a specific application. Due to the large size of the magnetic core used and the limited space in domestic annealing equipment, transverse annealing was adopted. Figure 4 These are the performance test curves of the magnetic core after annealing.

[0113] Figure 4 In the middle, the initial permeability μ of the magnetic core material i The maximum permeability μ reached 70,000 (>>10,000 threshold). m The remanent magnetic flux density is 530,000, and the remanent magnetic flux density is B. r The saturation magnetic induction intensity B is 0.1608T. s The capacitance is 0.488T, and the coercivity Hc is 0.2297A / m, which meets the actual performance requirements of the sensor.

[0114] The process of making the strip into a magnetic core is as follows: First, before heat treatment, spray (or brush) a high-temperature insulating oxide coating (magnesium oxide MgO or Al2O3) onto the strip for insulation; cut the strip into sheet structures of fixed length; spray (or brush) the oxide coating again; then place the strip into a fixture, and gently tap it with a soft rubber mallet to make the strip flat and aligned, with a total thickness of 13mm (the thickness dimension is consistent with the strip width); fix the fixture, impregnate and shape it, and dry it; finally, remove the fixture and cover it with a thin heat shrink tubing for protection.

[0115] The coil winding should be shorter than the magnetic core, with approximately 100mm of unused space at each end of the core. Special attention must be paid during core fabrication: each magnetic strip must be free of bending (or breakage), and the strips must be strictly aligned. The entire core should have a rectangular rod-like structure with neat ends (no bevels) and no burrs.

[0116] The magnetic core is designed to be 610 mm (24 in) long and is made of stacked strips of soft magnetic material, each 12.7 mm (0.5 in) wide. Each strip is approximately 13.68 μm thick (or thinner), and 650 strips are stacked together for a total thickness of 12.7 mm. Calculations and nuclear experiments show that the effective cross-sectional area of ​​the core is 0.000112903 m² when in a static, no-signal-input state. 2 (i.e., 112.903mm) 2 Assuming a fill factor of 70%, the equivalent diameter of the magnetic material is approximately 12 mm. At this point, the aspect ratio is approximately 50, and the effective permeability can reach over 700. Figure 5 This is a schematic diagram of the designed magnetic core.

[0117] Due to the varying widths of strip magnetic core materials used domestically and internationally (some in mm, others in inches), and the 12.7mm strip width conforming to international standards, the core material width was redesigned to 13mm. This saved on the cost of ordering new cutting tools when funds were limited. Due to limitations in domestic material forming technology, each strip was 20μm ± 5μm thick. The table below lists the actual machining dimensions of the sensor magnetic core.

[0118] long 610mm±0.2mm Width 13mm±0.2mm thick 13mm±0.2mm Temperature range -60℃- +80℃ Annealing temperature 340℃ Annealing method Longitudinal annealing initial permeability 70000 Maximum permeability 530000

[0119] In practical applications, the skeleton results are as follows:

[0120] The coil winding is divided into 16 sections with 17 partitions. Fifteen partitions are 4mm (±0.1mm) thick, and the other two are 10mm (±0.1mm) thick. These 17 circular partitions are fitted onto a hollow fiber tube and fixed to form a single coil frame, facilitating the fixation of the enameled wire. The partition spacing is 22.875mm (±0.1mm), as shown in the diagram. Figure 6 , Figure 7 , Figure 8 As shown;

[0121] A 610mm long, 13mm wide and thick magnetic core is placed inside a 616mm hollow fiber tube, with 3mm gaps at both ends. The gaps between the magnetic core and the tube wall are filled with epoxy adhesive (or unsaturated polyester resin with a hardener) that has good flowability, good temperature characteristics (no deformation from approximately -60℃ to 100℃), and a long curing time (>20 minutes) to ensure the magnetic core remains secure. The hollow fiber tube has a 1mm thick wall, an inner diameter of 19.80mm (0—+0.2mm with no lower tolerance), an outer diameter of 21.80mm (±0.2mm), and a length of 616mm. The fiber tube has high mechanical strength (shock resistance) and good temperature characteristics (no deformation). The partition groove is 3mm deep (±0.1mm) and 4mm wide (±0.1mm), with the two edges at the bottom of the groove rounded.

[0122] Specifically, the sensor feedback coil support sleeve, such as Figure 9 As shown. The overall structure of the sensor is as follows. Figure 10 As shown. The overall cross-section of the sensor structure is as follows. Figure 11 As shown.

[0123] The quasi-random winding method of the main induction coil reduces distributed capacitance, self-inductance, and mutual inductance. However, due to the presence of distributed capacitance, the coil's equivalent total loss resistance increases, and the quality factor decreases.

[0124] The main coil uses AWG 28 enameled wire, with the winding formed in one piece without any breaks. The impedance of the entire induction main coil is based on actual measurement. Using a quasi-random winding method, the enameled wire used in each CSAMT induction magnetic field sensor main coil exceeds 700g. The winding direction and overall structure of the induction main coil are as follows: Figure 12 , Figure 13 As shown in the table below. The parameters of AWG28 enameled wire are also shown in the table below.

[0125]

[0126] The feedback coil is made of 19mm wide copper foil, wound in the opposite direction to the main induction coil, for a total of 35 turns. Figure 14 As shown. Since copper foil is used as the feedback coil, it has its own shielding effect, so no other shielding method is needed. The added non-closed shielding strip can prevent the generation of induced magnetic fields.

[0127] The feedback coil is wound around the first layer of the sensor core frame sleeve, epoxy resin is added, and then 9 turns of calibration coil (copper enameled wire) are wound on top. Figure 15 As shown.

[0128] In terms of signal processing circuitry, the CSAMT inductive magnetic field sensor operates at high frequencies (0.1Hz-10kHz), therefore its low-noise amplifier circuit does not require chopper amplification technology, making the circuit relatively simple. The sensor's signal processing circuit primarily employs the principle of a flux negative feedback amplifier circuit, such as... Figure 16 As shown: Figure 16 The input has three terminals: the two output terminals "S" and "E" of the main induction coil, and the middle tap "C" of the main coil. The measured magnetic field signal is converted into a usable differential electrical signal by the magnetic field sensing component, then input to the preamplifier, and finally output as a signal V after passing through the second-stage amplification and filtering stage. out .

[0129] The magnetic feedback loop is mainly used to make the sensor have a flat amplitude-frequency characteristic curve over a wide frequency range, breaking through the limitation of the resonant frequency and achieving the purpose of expanding the sensor's bandwidth, without introducing additional circuit noise.

[0130] Throughout the circuit, the coil signal input, amplifier output, and power supply are all protected. To prevent strong magnetic field signals from saturating the preamplifier circuit, a limiting diode is connected at the circuit signal input (the current-limiting resistor can be added as needed). Amplifier output protection is primarily to prevent excessive sensor signals from damaging the data acquisition instrument. Power supply protection is to prevent short circuits caused by reversed power connections due to human error.

[0131] The preamplifier circuit is the first stage of amplification in a circuit. It mainly consists of three parts: a common-emitter differential amplifier circuit, an emitter constant current source, and a differential signal reference point stabilization circuit. An example of a preamplifier circuit for a CSAMT inductive magnetic field sensor is shown below. Figure 17 As shown.

[0132] In a common-emitter differential amplifier circuit, the key component is the super-match pair transistor, such as... Figure 17 As shown in Figures 1 and 2, the device used in the circuit is an LM394. Q1 and Q2 form a differential input stage, where the collector output of Q1 is V. c1 With input V i1呈 Antiphase relation, and V c1 With V c2 The circuit employs inverting voltage to amplify differential-mode signals and suppress common-mode signals, providing a dual-input, dual-output amplification mode. Diodes D1 and D2 protect the input from saturation when the voltage is too high, and the FD333 in the circuit limits the voltage by 1V. The emitter-guided constant current source (with extremely high equivalent internal resistance) stabilizes the quiescent operating point and effectively suppresses zero drift. Positive and negative power supplies compensate for the DC voltage drop across the emitter-guided constant current source and expand the output voltage range, ensuring the quiescent potential of the two bases is zero.

[0133] (1) When When the circuit is in a static state, i.e., in its static state, it is symmetrical, and at this time:

[0134]

[0135]

[0136]

[0137]

[0138] That is, when the input is 0, the output is also 0.

[0139] (2) When a differential signal is added, the signals at the two input terminals of the differential amplifier are equal in magnitude and opposite in polarity. If the circuit is perfectly symmetrical, assume V i1 Rise, V i2 If it decreases, then Ic1 When rising, I c2 The current decreases, therefore the magnitudes of the differential pair current increments are equal, i.e. The opposite polarity results in the voltage increment between the two output terminals and ground (i.e., the differential output voltage) ΔV. c1 With ΔV c2 Equal in size but opposite in polarity, and V c1 Decrease, V c2 The rise effectively amplifies the differential input signal. At this point, we have:

[0140]

[0141]

[0142] The dynamic resistance of the current source at the common emitter of the differential amplifier has no effect on differential-mode signals. With a perfectly symmetrical circuit and dual-input dual-output configuration, the load has the ability to suppress zero drift. The differential-mode voltage amplification factor is:

[0143]

[0144] Among them, R L This is the input resistance of the second-stage amplifier circuit. Differential input resistance R i That is, the equivalent resistance seen from the two input terminals, since R in this sensor circuit b The value is very small, therefore The differential output resistance R0 is the equivalent resistance seen from both output terminals. Therefore, R0 and R i It is twice that of a single tube.

[0145] Common mode rejection ratio K CMR It is an important specification of differential amplifiers, measured in dB, and the formula is:

[0146]

[0147] Because it uses a dual-ended output format, K is considered to be... CMR infinity; This is the common-mode voltage amplification factor.

[0148] The current source is an LM234, which provides the DC operating point for the transistor. Let the resistor R... 14 The voltage across the terminals is V R The voltage across the diode is V. D The current I of the current source set It is the sum of I1 and I2, each accounting for approximately 50% of the current value. bias It is usually included in I1, and during calculation, V is made RThe value increased by 5.9%.

[0149]

[0150] in,

[0151]

[0152]

[0153] The DC path and small-signal equivalent circuit of the stable circuit in the preamplifier are as follows: Figure 18 and Figure 19 As shown.

[0154] Assuming in the circuit, Then the collector-emitter voltage is:

[0155]

[0156]

[0157]

[0158] Ignore V BEQ ,have:

[0159]

[0160] In the circuit, the collector quiescent current I CQ Only with DC voltage V ee and resistance R 18 related. β As temperature changes, I CQ Basically unchanged, base current .in, β This is the current amplification factor, which is related to the characteristics of the transistor device.

[0161] The second-stage amplifier and filter circuit of the sensor is as follows: Figure 20 As shown. The amplifier circuit mainly uses the LT1457 chip and a symmetrical "T-type resistor network," and also functions as a low-pass filter. D3 and D4 in the circuit provide overvoltage protection (within ±15V of the output signal). Assuming... , , , Through circuit analysis, solving the system of equations yields the following expression:

[0162]

[0163] make Then the above formula can be written as:

[0164]

[0165] Specifically, the main parameters of the inductive magnetic field sensor are shown in the table below:

[0166]

[0167] The computer-readable storage medium may be any combination of one or more readable media. A readable medium may be a readable signal medium or a readable storage medium. A readable storage medium may be, for example, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination thereof. More specific examples of readable storage media (a non-exhaustive list) include: an electrical connection having one or more wires, a portable disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage device, magnetic storage device, or any suitable combination thereof.

[0168] The above description has been given for purposes of illustration and description. Furthermore, this description is not intended to limit the embodiments of this application to the forms disclosed herein. Although numerous exemplary aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations thereof.

Claims

1. A miniaturized broadband inductive magnetic field sensor, comprising a magnetic core, an induction coil wound on the magnetic core, a feedback coil, and a low-noise signal processing circuit electrically connected to the induction coil, characterized in that: The magnetic core is a long rod-shaped structure formed by laminating and curing high-permeability soft magnetic tape. The length of the magnetic core is 580mm to 640mm, and the cross-section of the magnetic core is a square or equivalent circle with a side length of 11mm to 15mm. The feedback coil is formed by spirally winding a metal foil strip along the length of the magnetic core. The metal foil strip also constitutes the main shielding layer in the sensor to suppress external electric field interference. The feedback coil is connected to the output terminal of the low-noise signal processing circuit and the induction coil, respectively.

2. The miniaturized wideband inductive magnetic field sensor according to claim 1, characterized in that The high permeability soft magnetic tape is a cobalt-based amorphous or nanocrystalline alloy tape, and the magnetic core is subjected to longitudinal magnetic field annealing treatment at 300°C to 380°C, with an initial permeability of not less than 50,000.

3. The miniaturized wideband inductive magnetic field sensor according to claim 2, characterized in that The magnetic core has a length of 610mm ± 0.2mm and a cross-section that is a square with a side length of 13mm ± 0.2mm.

4. The miniaturized broadband inductive magnetic field sensor according to claim 1, characterized in that, The magnetic core has a fill factor of more than 70%, and the interlayer of the flexible magnetic tape is coated with a high-temperature insulating oxide coating.

5. The miniaturized broadband inductive magnetic field sensor according to claim 1, characterized in that, The induction coil is wound on the frame using a quasi-random winding method or a segmented winding method. The frame is fitted outside the magnetic core and divides the induction coil into multiple segments.

6. The miniaturized broadband inductive magnetic field sensor according to claim 5, characterized in that, The frame includes multiple parallel partitions that divide the induction coil into 14 to 18 segments, with a spacing of 20 mm to 25 mm between adjacent partitions.

7. The miniaturized broadband inductive magnetic field sensor according to claim 1, characterized in that, The metal foil strip is copper foil with a width of 15mm to 25mm, and the feedback coil has 30 to 40 turns.

8. The miniaturized broadband inductive magnetic field sensor according to claim 7, characterized in that, A calibration coil is also wound outside the feedback coil.

9. The miniaturized broadband inductive magnetic field sensor according to claim 1, characterized in that, The low-noise signal processing circuit includes a preamplifier stage and an amplification and filtering stage; The preamplifier stage includes a differential amplifier circuit composed of super-matched differential pairs and a constant current source circuit. The amplification and filtering stage is electrically connected to the preamplifier stage and includes an operational amplifier and a T-type filter network composed of resistors and capacitors.

10. The miniaturized broadband inductive magnetic field sensor according to claim 1, characterized in that, The sensor operates in the frequency range of 0.1Hz to 10kHz, has a noise floor of less than 10 fT / √Hz at 1kHz, weighs less than 4kg, and has a maximum outer diameter of less than 65mm.

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