A fluxgate probe

Abstract

The present application relates to the technical field of measuring magnetic variable, especially to a fluxgate probe, which is based on a flexible printed circuit substrate, and includes four signal layers on the flexible printed circuit substrate, from bottom to top, the four signal layers are: a wiring layer, which is provided with a trace for providing an excitation signal; a magnetic core mounting and coil lower layer, which is located on the wiring layer and is used for welding a magnetic core layer; and a coil upper layer, which is located above the magnetic core layer and is used for circuit closure with the magnetic core mounting and coil lower layer to form an induction coil. Compared with the existing fluxgate probe design, the probe structure described in the present application is based on FPC, and has the characteristics of flatness, easy integration and flexibility. It can adapt to the demand for compact integration of flexible and wearable devices, and the probe can expand the application field of fluxgate.

Description

Technical Field

[0001] This invention relates to the field of magnetic variable measurement technology, specifically a fluxgate probe. Background Technology

[0002] Fluxgate magnetometers are the primary instruments for magnetic field measurement, capable of measuring three-component space vector magnetic fields. They offer advantages such as low power consumption, small size, high accuracy, and high reliability, and are currently widely used in aviation, aerospace, and ground-based magnetic field measurement fields.

[0003] Fluxgate magnetometers convert low-frequency magnetic field signals in space into electrical signals using an excitation coil and an induction coil, leveraging the fluxgate effect of a soft magnetic core. To improve the accuracy of fluxgate magnetometer measurements of spatial magnetic fields, their induction coils typically possess very high sensitivity, enabling precise vector detection of external magnetic fields.

[0004] Generally, an open-loop fluxgate magnetometer probe consists of three main components: a magnetic core, an excitation coil, and an induction coil. In addition, there are various structural components that support and mount these three main components. The magnetic core is made of a soft magnetic alloy, whose hysteresis loop exhibits characteristics of very high initial permeability, very low saturation permeability, and relatively low coercivity. The excitation coil, under the action of an excitation current, generates an excitation magnetic field, causing the magnetic core to periodically saturate. Due to the fluxgate effect, this periodic saturation is asymmetrical when the ambient magnetic field is not zero. This asymmetrical magnetic field signal is picked up by the induction coil, forming a secondary induced electromotive force signal carrying information about the ambient magnetic field.

[0005] Fluxgate probes can be classified into two types based on the spatial relationship between the cross-sectional directions of the excitation coil and the induction coil: parallel fluxgate and orthogonal fluxgate. The similarity lies in the fact that in both structures, the direction of the induction coil is parallel to the vector component of the external magnetic field being measured. The difference lies in the direction of the excitation and induction coils. In a parallel fluxgate, the excitation coil generates an excitation magnetic field parallel to the vector component of the external magnetic field being measured. This excitation magnetic field causes the magnetic core to periodically saturate in the direction of the vector component of the external magnetic field being measured, and the degree of asymmetry in this periodic saturation is determined by the external magnetic field being measured. In an orthogonal fluxgate, the excitation coil is orthogonal to the induction coil, generating a magnetic field along the circumferential direction of the induction coil, orthogonal to the vector direction of the external magnetic field being measured. The excitation magnetic field causes the magnetic core to periodically saturate in the direction perpendicular to the vector component of the external magnetic field being measured, and the degree of saturation remains symmetrical. However, the projection of the saturated magnetic field onto the axial direction of the induction coil is determined by the external magnetic field being measured.

[0006] Based on orthogonal fluxgates, a fundamental frequency operating mode orthogonal fluxgate has been developed. This type of fluxgate's excitation magnetic field has a DC bias, allowing it to oscillate near the saturation point, rather than between positive and negative saturation points. This configuration effectively suppresses Barkhausen noise caused by core domain oscillations, reducing the overall noise level of the probe. Generally, in the fundamental frequency operating mode of the orthogonal fluxgate, the magnetic core also acts as the excitation coil, with the excitation current signal directly applied to the core. The current flowing through the core causes the core's own magnetic flux to saturate.

[0007] Generally, the even-order harmonic signals in the output signals of the induction coils of parallel and quadrature fluxgate magnetometers carry information about the external magnetic field strength to be measured. Even-order harmonic signals refer to signals with frequencies even multiples of the excitation signal. However, for quadrature fluxgate magnetometers operating in fundamental frequency mode, the output signal of the induction coil carrying information about the external magnetic field to be measured has the same frequency as the excitation signal.

[0008] Generally, fluxgate coils are made of enameled wire and are fixed to the magnetic core by combining various auxiliary materials and structural components. They are usually relatively large in size, which is not conducive to integration into small wearable devices. Summary of the Invention

[0009] The purpose of this invention is to provide a fluxgate probe to solve the problems mentioned in the background art.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] A fluxgate detector, based on a flexible printed circuit substrate, includes four signal layers on the flexible printed circuit substrate, from the bottom layer to the top layer:

[0012] The wiring layer contains traces for providing excitation signals;

[0013] The core mounting and coil underlayer, located on the wiring layer, is used for soldering the core layer;

[0014] The upper layer of the coil, located above the magnetic core layer, is used for mounting the magnetic core and closing the lower layer of the coil to form an induction coil;

[0015] The magnetic core layer has a flat quadrilateral cross-section, and the magnetic core layer works in conjunction with the flexible printed circuit to construct an orthogonal fluxgate.

[0016] Furthermore, the wiring layer includes a core mounting pad, an excitation signal input pad, and an induction signal output pad.

[0017] Furthermore, the core mounting and coil lower layer includes an excitation signal input pad, a core mounting pad, an induction signal output pad, an induction coil, and a coil signal return line.

[0018] Furthermore, the magnetic core is welded to two magnetic core mounting pads at both ends by pulse cold soldering. Each turn of the induction coil is divided into upper and lower half-turns. The lower half-turn is printed on this layer with oblique wiring. The pads are distributed on both sides of the reserved position on the magnetic core. The left and right pads are parallel in the horizontal direction. The coil signal return line is led back from the end point of the lower half-turn to the upper induction signal output pad.

[0019] Furthermore, the magnetic core mounting pads can mount one or more thin strip magnetic cores. The lower half-turn oblique coil wiring starts and ends with the pads on both sides intersecting. The pads have solder mask openings, the wiring part is covered with oil, and the two magnetic core mounting pads, the two excitation signal input pads and the two induction signal output pads are via pads.

[0020] Furthermore, the pads on the upper layer of the coil are the same size as those on the lower layer and correspond one-to-one. The traces on the upper layer are parallel traces with the same diameter as those on the lower layer.

[0021] Furthermore, the four signal layers on the flexible printed circuit substrate are fabricated as follows:

[0022] Step 1: After the wiring layer, magnetic core, and lower coil layer are installed, solder paste is applied to them using a stencil, following the requirements of the SMT process.

[0023] Step 2: Lay nickel strips at the locations where the magnetic core will be installed to reserve space;

[0024] Step 3: Mount the upper layer of the coil onto the corresponding positions of the magnetic core mounting and the lower layer of the coil, and secure it.

[0025] Step 4: Securely solder the upper layer of the coil to the magnetic core and the lower layer of the coil.

[0026] Step 5: Check the welding quality and the continuity of the coil circuit;

[0027] Step 6: Stack and pre-weld multilayer soft magnetic core strips using a pulsed cold welding process;

[0028] Step 7: Remove the nickel strip from Step 2 and replace it with a multilayer soft magnetic core strip;

[0029] Step 8: Using a pulsed cold soldering process, solder the soft magnetic core strip onto the core mounting pads on the core mounting and coil lower layer.

[0030] Furthermore, in step 2, the thickness of the nickel strip is greater than the thickness of the magnetic core to be installed, but less than 1.5 times the thickness of the magnetic core to be installed.

[0031] Furthermore, in step 2, high-temperature resistant tape or SMT red glue is used for additional fixation.

[0032] Furthermore, in step 4, pulsed cold soldering reflow soldering or wave soldering is performed, the upper layer of the coil is installed with the magnetic core, and the lower layer of the coil is soldered.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] Compared to existing fluxgate detector designs, the detector structure described in this invention is based on FPC (Flexible Printed Circuit), featuring a flat surface, easy integration, and flexibility. This allows it to meet the space-constrained integration requirements of flexible, wearable devices.

[0035] Compared to the main magnetic field sensors currently used in wearable devices, such as Hall sensors and giant magnetoresistive sensors, fluxgate sensors can provide more accurate and sensitive vector magnetic field detection capabilities.

[0036] Traditional fluxgate magnetometers are typically used in scientific and exploration work, while the fluxgate probe based on the flexible printed circuit substrate of this invention can expand the application fields of fluxgate magnetometers. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the design and dimensions of the front copper layer of the FPC in this invention.

[0038] Figure 2 This is a schematic diagram of the copper layer design on the back of the FPC of the present invention.

[0039] Figure 3 This is a schematic diagram of the upper layer of the coil of the present invention and its dimensions.

[0040] Figure 4 This is an abstract diagram of the overall structure of the present invention.

[0041] Figure 5 This is a three-dimensional design concept diagram of the present invention.

[0042] Figure 6 This is a rendering of the second layer of the probe of the present invention.

[0043] Figure 7 This is a rendering of the first layer of the probe of this invention.

[0044] Figure 8 This is a rendering of the fourth layer of the probe of this invention.

[0045] Figure 9 This is a diagram of the copper layer of the first layer of the probe of this invention.

[0046] Figure 10 This is a diagram of the mask layer of the probe of the present invention, which is the first layer.

[0047] Figure 11 This is a diagram of the copper layer of the second layer of the probe of this invention.

[0048] Figure 12This is a diagram of the mask layer of the second layer of the probe of the present invention.

[0049] Figure 13 This is a diagram of the fourth copper layer of the probe of this invention.

[0050] Figure 14 This is the mask layer of the fourth layer of the probe in this invention.

[0051] Figure 15 This is a schematic diagram of the installation process of the present invention.

[0052] Figure 16 This is a schematic diagram showing the cold soldering of the magnetic core onto two pads for the present invention.

[0053] Figure 17 This is a schematic diagram illustrating how the fourth layer is stacked on top of the second layer and welded together, as per the present invention.

[0054] Figure 18 This is a schematic diagram showing the stacking relationship between the layers after the installation of the present invention.

[0055] In the diagram: 1-wiring layer, 2-core mounting and lower coil layer, 3-core layer, 4-upper coil layer. Detailed Implementation

[0056] 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.

[0057] In the description of this invention, it should be noted that the terms "upper end," "lower end," "inner," "outer," "front end," "rear end," "both ends," "one end," and "the other end," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. In addition, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0058] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed," "equipped with," "sleeved with," "connected," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0059] Please see Figure 1-18 The present invention provides a technical solution:

[0060] This invention relates to an orthogonal fluxgate magnetic sensor configuration based on the fundamental frequency operating mode, and designs a fluxgate probe fabricated on a flexible printed circuit (FPC) substrate, and describes its main manufacturing process.

[0061] This invention addresses the technical problem of fluxgate sensors being too large to be integrated into small wearable devices. These wearable devices include, but are not limited to, smartwatches, portable biomagnetometers, and cardiac magnetograph arrays.

[0062] The basic principle of this invention is to reduce the three-dimensional structure of a fundamental frequency-operating orthogonal fluxgate probe to two dimensions: flattening the original three-dimensional structure. The cylindrical fluxgate core is replaced with a thin strip core, changing the core's cross-section from a circle to a flattened quadrilateral. The coil wound around the core is then made to match the core's shape, also changing its cross-section from a circle to a flattened quadrilateral. Thus, a quasi-planar circuit structure is used to realize the coil, core, etc., of a traditional fluxgate, thereby constructing a fluxgate probe for quasi-static magnetic field sensing.

[0063] The technical solution of this invention lies in laying the induction coil of the fluxgate magnetometer on a flexible printed circuit (FPC) substrate in a wiring manner, and spot-soldering a thin strip magnetic core onto the corresponding pads of the FPC to construct an orthogonal fluxgate magnetometer. By applying an AC current signal with DC bias to the magnetic core, this orthogonal fluxgate magnetometer is made to operate in the fundamental frequency operating mode.

[0064] The flexible circuit substrate referred to in this invention is the polyester film structure of the FPC itself, which includes the induction coil, induction coil auxiliary traces, magnetic core fixing pads, magnetic core current auxiliary traces, anti-interference copper mesh, and the induction coil itself. The thin strip magnetic core referred to in this invention is a thin strip approximately 20 micrometers thick, made of soft magnetic alloy crystal or soft magnetic amorphous alloy.

[0065] Compared to existing fluxgate detector designs, the detector structure described in this invention is based on FPC (Flexible Printed Circuit), featuring a flat surface, easy integration, and flexibility. This allows it to meet the space-constrained integration requirements of flexible, wearable devices.

[0066] Compared to the main magnetic field sensors currently used in wearable devices, such as Hall sensors and giant magnetoresistive sensors, fluxgate sensors can provide more accurate and sensitive vector magnetic field detection capabilities.

[0067] Traditional fluxgate magnetometers are typically used in scientific and exploration work, while fluxgate probes with flexible printed circuit boards can expand the application areas of fluxgate magnetometers.

[0068] like Figure 1 As shown, the magnetic core mounting and lower coil layer 2 is the second layer of the probe, which is also the design diagram of the top copper layer of the FPC printed circuit. Solid filled patterns represent traces, and hollow patterns represent pads. The traces are covered with an insulating layer, while the pads are not. The diagram includes the main components such as the induction signal output pad, the bottom trace of the induction coil, the induction signal return trace, the excitation signal input pad, and the magnetic core mounting pad, along with their dimensions.

[0069] like Figure 2 As shown, wiring layer 1 is the first layer of the probe, which is also the design diagram of the bottom copper layer of the FPC printed circuit. The solid fill pattern represents the traces.

[0070] like Figure 3 As shown, layer 4 on top of the coil is the design diagram for the fourth layer of the probe. The dashed lines represent traces, which are covered with an insulating layer. The solid lines outside the dashed lines are solder pads used for surface mount technology.

[0071] like Figure 4 The diagram shown is an abstract structural diagram of the probe described in this invention. The fundamental purpose of all the processes and designs described in this invention is to realize the orthogonal fluxgate magnetic sensor in fundamental frequency operating mode as depicted in the diagram.

[0072] like Figure 5 The image shown is a 3D concept drawing of the FPC probe described in this invention after assembly. The concept drawing only includes the upper and lower sides of the induction coil, the pads connecting the two sides, and the multi-layered thin strip magnetic core. The scale of the concept drawing is not entirely equivalent to the scale of the finished product.

[0073] like Figure 6 The image shown is a rendered image of the second layer of the probe, i.e., the top layer of the FPC. The rendered image is the same scale as the actual product, but the colors are for reference only.

[0074] like Figure 7 As shown, this is a rendering of the finished product of the probe's first layer, which is the bottom layer of the FPC.

[0075] like Figure 8The image shown is a rendering of the final product on the fourth layer of the probe.

[0076] Specifically, the design described in this invention plans out a typical fundamental frequency mode orthogonal fluxgate into four signal layers, from bottom to top: wiring layer 1; core mounting and lower coil layer 2; core layer 3; and upper coil layer 4.

[0077] The wiring layer mainly contains the traces for the excitation signals, such as... Figure 2 .

[0078] Core mounting and lower coil layer 2, as shown Figure 1 The magnetic core (layer) is soldered at both ends to two core mounting pads using pulse cold soldering. The core mounting pads are 2mm wide and can accommodate one or more thin strip magnetic cores ranging from 2mm wide to 33mm long and 25mm short. Each turn of the induction coil is divided into upper and lower halves, with the lower half printed on this layer using a diagonal wiring pattern. Each end of the wiring has a 0.3mm wide pad, distributed on both sides of the reserved position on the magnetic core. The pads on both sides are parallel horizontally, with a 4.7mm spacing and an outer width of 7.3mm. There are 20 pads on each side, evenly distributed vertically, with a 0.2mm gap between each pair of pads. The diagonal coil wiring of the lower half starts and ends at the staggered pads on both sides, as shown in the figure. The pads have solder mask openings, and the wiring is covered with solder mask. Furthermore, the coil signal return line is led back from the end point of the lower half to the upper induction signal output pad. Two magnetic core mounting pads, two excitation signal input pads, and two induction signal output pads are via pads, which facilitate the cold soldering process of the magnetic core and subsequent installation and integration. Figure 1 and Figure 2 The via pads in the diagram correspond one-to-one.

[0079] Core layer 3, located between the lower and upper coil layers, is positioned to ensure the core is enclosed within the induction coil. Due to the use of a thin-film core, the initial permeability of the core material used here needs to be very high, such as Vitrovac 6025 (room temperature, high sensitivity) or Vitroperm 800P (high temperature operating stability). Such soft magnetic alloys generally cannot withstand conventional soldering temperatures; therefore, the core is soldered to the core mounting pads using a low-temperature pulse cold soldering method. Depending on the required signal-to-noise ratio and sensitivity for the measurement, one or more core films can be stacked.

[0080] upper layer 4 of the coil, such as Figure 3 By connecting the pads of the upper and lower layers of the coil above the magnetic core layer, the upper and lower layer circuits of the coil are closed, forming an effective and complete induction coil. The pads of the upper layer of the coil are the same size as those of the lower layer. The traces of the upper layer are parallel traces with the same wire diameter as those of the lower layer. The outer width of the upper layer of the coil is 7.2mm, and its pads correspond one-to-one with the pads of the lower layer of the coil, and the whole is surface-mount soldered.

[0081] The four layers together form a structure like this Figure 4 The orthogonal fluxgate structure is shown. Its 3D design concept diagram is shown below. Figure 5 .

[0082] This probe structure can be fabricated as an independent FPC circuit or integrated into a complete circuit.

[0083] The probe's fabrication process generally follows a workflow similar to SMT (Surface Mount Technology). Layers 1 and 2 of the four-layer circuit are fabricated using FPC (Flexible Printed Circuit), layer 3 is a pre-fabricated soft magnetic material strip, and layer 4 is fabricated separately using FPC. The following steps are then followed:

[0084] ① After the first and second layers are completed, solder paste is applied to them using a stencil, following the requirements of the SMT process.

[0085] ② Lay nickel strips at the location where the magnetic core is to be installed to reserve space. The thickness of the nickel strips is greater than the thickness of the magnetic core to be installed, but less than 1.5 times the thickness of the magnetic core to be installed.

[0086] ③ Mount the fourth layer in the corresponding position on the second layer, and use high-temperature resistant tape or SMT red glue for additional fixation;

[0087] ④ Perform reflow soldering or wave soldering to ensure a strong bond between the 4th layer and the 2nd layer;

[0088] ⑤ Inspect the welding quality and the continuity of the coil circuit;

[0089] ⑥Layered and pre-welded with multilayer soft magnetic core strips using pulse cold welding process;

[0090] ⑦ Remove the nickel strip from step ② and replace it with a multilayer soft magnetic core strip.

[0091] ⑧ The soft magnetic core strip (i.e., the third layer) is welded to the core mounting pad of the second layer using a pulse cold welding process.

[0092] Except for the pulse cold soldering process and the nickel strip-core replacement process, the above-mentioned processes can all be automated, and are similar to the SMT processing technology of other electronic components, which reduces the difficulty of batch production and integration.

[0093] The completed FPC probe works in conjunction with the relevant excitation and sampling circuits of a conventional fundamental frequency mode orthogonal fluxgate. This is not the subject of protection in this invention and will not be described further.

[0094] Through the above-described manner, the present invention provides a fluxgate probe for a flexible printed circuit substrate.

[0095] This invention relates to a fundamental frequency mode orthogonal fluxgate probe on a flexible printed circuit substrate; however, it does not protect the general structure and principle of the fundamental frequency mode orthogonal fluxgate probe, nor does it protect the general drive and sampling circuit of the fundamental frequency mode orthogonal fluxgate magnetometer.

[0096] This invention relates to the specific process flow for manufacturing a fluxgate probe on a flexible printed circuit substrate, including stencil-solder paste process, nickel bar placement, SMT and soldering, magnetic core pre-soldering, magnetic core replacement of placement nickel bar, low-temperature spot soldering, etc.; but does not protect individual steps in the process flow such as general SMT process and pulsed low-temperature spot soldering process.

[0097] In this invention, both the first and second layers of the probe have pads and traces, such as... Figures 9 to 14 : Figure 9 In the middle, the pad on the right is the pad connected to the ground line of the shielding layer. The shielding layer is a separate circuit network used to prevent high-frequency interference. To avoid complexity, the shielding layer (copper plating) in the wiring is hidden here. Figure 10 In this section, the mask layer corresponds to the copper layer mentioned above. The mask is the negative of the solder mask; its presence means the solder mask is absent, which means the copper layer is exposed here, forming the solder pads. Additionally, the four round holes at the corners are mounting holes. Figure 11 Similarly, to avoid complexity, the shielding layer (copper plating) in the wiring is hidden. Figure 12 In this layer, there is no copper shielding.

[0098] This invention, such as Figures 15 to 18 The diagram in the middle illustrates the installation process, showing the stacking relationship between the three layers.

[0099] The probe working mode of this invention follows the working principle of the "Orthogonal Fluxgate Magnetometer in Fundamental Mode" proposed by Ichiro Sasada of Kyushu University in 2001.

[0100] a) First, the electrical structure of the probe is similar to that of a traditional orthogonal fluxgate magnetometer, that is: the excitation current flows directly through the magnetic core along the axial direction of the magnetic core, or through the wires embedded in the magnetic core; the axis of the induction coil coincides with the axis of the magnetic core.

[0101] (b) The fluxgate magnet uses a soft magnetic core. Soft magnetic materials exhibit a "fluxgate effect," where their permeability changes with the external magnetic field. When the external magnetic field is small, the core exhibits ferromagnetism with very high permeability; when the external magnetic field is large and exceeds the saturation threshold, the core exhibits paramagnetism, and the permeability drops sharply. In terms of magnetic flux, the flux within the core initially increases rapidly with increasing external magnetic field, but once the external magnetic field exceeds the threshold, the flux within the core almost no longer increases with further increases in the external magnetic field. This effect is called the fluxgate effect.

[0102] c) Under this setting, the excitation current excites the circumferential excitation magnetic field of the magnetic core; the excitation magnetic field is superimposed on the external magnetic field to be measured B0, thereby causing the magnetic core to saturate and inducing the fluxgate effect.

[0103] d) Because the excitation magnetic field is oriented along the core circumference while the induction coil is oriented along the core axis, only the projection of the external magnetic field B0 onto the core axis can be measured. That is, the components of the excitation magnetic field and the measured magnetic field are orthogonal. Hence the name orthogonal fluxgate.

[0104] e) The excitation current of a traditional orthogonal fluxgate magnetometer is periodically symmetrical, and therefore the excitation magnetic field it generates is also periodically symmetrical. However, after superimposing an external magnetic field B0, the magnetic field experienced by the core will be periodically asymmetrical. This will induce the core to repeatedly saturate in both positive and negative magnetic fields, resulting in a periodic asymmetrical saturation.

[0105] f) The aforementioned asymmetric saturation of the magnetic core is related to the strength and direction of the external magnetic field B0 to be measured. Since the axis of the induction coil is fixed, the induction coil will mainly pick up the projection of this magnetic flux change onto the axis of the induction coil. The induced electromotive force (EMF) on the induction coil is proportional to the rate of change of magnetic flux within the magnetic core. When the magnetic core is saturated, the rate of change of magnetic flux is very small, and the induced EMF is very small. When the magnetic core is unsaturated, the rate of change of magnetic flux is very large, and the induced EMF is very large. By monitoring the periodic asymmetric changes in the induced EMF or the periodic asymmetric changes in the induced current, the strength of the external magnetic field B0 to be measured can be calculated.

[0106] g) Unlike traditional quadrature fluxgates, the excitation current of a fundamental frequency-operating quadrature fluxgate is a periodic sinusoidal current superimposed with a sufficiently large bias current. This results in the excitation magnetic field being a superposition of a large DC magnetic field and a smaller oscillating AC magnetic field. This induces the magnetic core to oscillate repeatedly around a saturation point, rather than undergoing alternating positive and negative saturation; that is, it is a periodic, unidirectional saturation.

[0107] h) Since the component of the external magnetic field B0 to be measured is always orthogonal to the excitation magnetic field, the superimposed magnetic field of the external magnetic field B0 and the excitation magnetic field is always greater than the excitation magnetic field, regardless of the direction of the external magnetic field B0. Therefore, the stronger the external magnetic field B0 to be measured, the deeper the saturation depth of the magnetic core and the longer the saturation time.

[0108] i) The projection of the direction of core saturation onto the core axis is consistent with the projection of the external magnetic field B0 onto the core axis. Therefore, the rate of change of the projection of the magnetic flux within the core onto the induction coil axis is related to the intensity of the projection of the external magnetic field B0 onto the induction coil axis, while its direction is consistent with the external magnetic field.

[0109] j) Based on this setting, the strength of the external magnetic field to be measured can be calculated by monitoring the magnitude and direction of the induced electromotive force on the induction coil.

[0110] k) Therefore, in general, in this invention, after passing an alternating current with a DC bias through the magnetic core, the magnitude and direction of the external magnetic field component along the axis of the induction coil (which is also the axis of the magnetic core) can be measured by measuring the amplitude and direction of the induced electromotive force on the induction coil.

[0111] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A manufacturing process for a fluxgate magnetometer probe, the fluxgate magnetometer probe being based on a flexible printed circuit, the flexible printed circuit comprising four signal layers, from the bottom layer to the top layer as follows: The wiring layer (1) is provided with traces for providing excitation signals; The core mounting and lower coil layer (2) is located on the wiring layer (1) and is used to solder the core layer (3). The upper coil layer (4) is located above the magnetic core layer (3) and is used to install the magnetic core and close the loop of the lower coil layer (2) to form an induction coil; Its features are, The four signal layers on the flexible printed circuit substrate are fabricated as follows: Step 1: After the wiring layer (1), magnetic core mounting and coil lower layer (2) are completed, solder paste is applied to them with the help of a stencil; Step 2: Lay nickel strips at the locations where the magnetic core will be installed to reserve space; Step 3: Mount the upper coil layer (4) to the corresponding positions of the magnetic core mounting and the lower coil layer (2), and fix it in place; Step 4: Securely weld the upper coil layer (4) to the magnetic core and the lower coil layer (2); Step 5: Check the welding quality and the continuity of the coil circuit; Step 6: Stack and pre-weld multilayer soft magnetic core strips using a pulsed cold welding process; Step 7: Remove the nickel strip from Step 2 and replace it with a multilayer soft magnetic core strip; Step 8: Using pulse cold welding process, weld the soft magnetic core strip onto the core mounting pad of the core mounting and coil lower layer (2).

2. The manufacturing process of the fluxgate probe as described in claim 1, characterized in that, The wiring layer (1) includes a magnetic core mounting pad, an excitation signal input pad, and an induction signal output pad.

3. The manufacturing process of the fluxgate probe as described in claim 1, characterized in that, The core mounting and lower coil layer (2) includes an excitation signal input pad, a core mounting pad, an induction signal output pad, an induction coil, and a coil signal return line.

4. The manufacturing process of the fluxgate probe as described in claim 3, characterized in that, The magnetic core is soldered to two magnetic core mounting pads at both ends by pulse cold soldering. Each turn of the induction coil is divided into upper and lower half-turns. The lower half-turn is printed on this layer with diagonal wiring. The pads are distributed on both sides of the reserved position on the magnetic core. The left and right pads are parallel in the horizontal direction. The coil signal return line is led back from the end point of the lower half-turn to the upper induction signal output pad.

5. The manufacturing process of the fluxgate probe as described in claim 4, characterized in that, One or more thin strip magnetic cores are mounted on the core mounting pads. The lower half-turn oblique coil wiring starts and ends at the intersection of the two side pads. The pads are opened with solder mask and the wiring is covered with oil. There are two core mounting pads, two excitation signal input pads and two induction signal output pads, which are via pads.

6. The manufacturing process of the fluxgate probe as described in claim 1, characterized in that, The pads on the upper layer (4) of the coil are the same size as the pads on the lower layer and correspond one-to-one. The traces on the upper layer are parallel traces with the same diameter as those on the lower layer.

7. The manufacturing process of the fluxgate probe as described in claim 1, characterized in that, In step 2, the thickness of the nickel strip is greater than the thickness of the magnetic core to be installed, but less than 1.5 times the thickness of the magnetic core to be installed.

8. The manufacturing process of the fluxgate probe as described in claim 1, characterized in that, In step 2, high-temperature resistant tape or SMT red glue are used for fixation.

9. The manufacturing process of the fluxgate probe as described in claim 1, characterized in that, In step 4, pulse cold soldering reflow soldering or wave soldering is performed, and the upper layer (4) of the coil is soldered to the magnetic core and the lower layer (2) of the coil.

Images