A printed PCB-based triaxial capacitor sensor and its assembly method

Abstract

The application belongs to the technical field of capacitive sensors, and particularly relates to a three-coaxial capacitive sensor based on a printed PCB and an assembling method thereof. The sensor forms potential layers of a measuring electrode, an equipotential protection electrode and a shielding electrode in a multilayer PCB, and suppresses a connection parasitic capacitance through a bottom local Faraday cage and a shielding fixing part. The sensor is a three-coaxial potential structure including the measuring electrode, the protection electrode and the shielding electrode, and the measuring end, the protection end and the shielding end maintain clear spatial hierarchy and potential relationship at a working surface, inboard wiring, a bottom welding end and a connection place of an external cable. The application considers assembling positioning, shielding connection and processability of a machining fixing part while reducing the connection end parasitic capacitance.

Description

Technical Field

[0001] This invention belongs to the field of capacitive sensor technology, specifically relating to a three-coaxial capacitive sensor based on a printed PCB and its assembly method, and particularly to a sensor structure that forms a potential layer of measuring electrode, equipotential protection electrode and shielding electrode in a multilayer PCB, and suppresses connection parasitic capacitance through a bottom local Faraday cage and shielding fixing component. Background Technology

[0002] Capacitive sensors feature non-contact measurement, compact structure, high sensitivity, and high resolution, making them suitable for applications such as minute displacement, gap changes, proximity detection, and precision measurement. For capacitance changes on the order of femtofarads or even smaller, the sensor probe structure, connecting cables, and detection circuitry all affect the final output, with parasitic capacitance at the probe tip, edge effects, and external interference being particularly critical.

[0003] Traditional high-precision capacitive sensor probes often employ mechanical processing to form an approximately three-coaxial structure, where the measuring electrode, protective electrode, and shielding electrode form a relatively complete coaxial or surrounding relationship in space. The measuring electrode is used to form the capacitance to be measured with the conductor being measured; the protective electrode is typically driven by the detection circuit to a potential close to the measuring end to weaken the edge electric field and cable parasitic capacitance; and the shielding electrode is connected to a reference ground or shielding terminal to isolate external interference.

[0004] However, machining triaxial probes typically presents challenges such as high processing difficulty, small insulation gaps, numerous parts, complex welding and assembly, long processing cycles, and high costs. Fabricating sensor probes using PCB printing technology leverages mature copper foil patterning, lamination, via processing, and surface treatment techniques, improving structural consistency and shortening prototype iteration cycles.

[0005] However, PCB capacitance probes cannot simply be planarized compared to traditional triaxial probes. PCB copper foil is thin, and dielectric coupling exists in the substrate. Through-holes, pads, pin headers, screws, and fasteners can all introduce additional parasitic capacitance. Especially during the process of leading the measurement end from the working surface to the bottom pad and connecting the triaxial cable, if the measurement trace or solder joint is directly exposed near the shielding end, the change in the measured capacitance will be overwhelmed by the connected parasitic capacitance. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a triaxial capacitive sensor based on printed PCB and its assembly method. It utilizes multilayer PCB to form a triaxial potential structure of measuring electrode, protection electrode and shielding electrode, so that the measuring end, protection end and shielding end maintain a clear spatial hierarchy and potential relationship on the working surface, in-board traces, bottom soldering end and external cable connection. While reducing parasitic capacitance at the connection end, it also takes into account the assembly positioning, shielding connection and machinability of the machined fasteners.

[0007] The first aspect of the present invention discloses a triaxial capacitive sensor based on a printed PCB, comprising: a PCB capacitive probe, a partial Faraday cage, a triaxial cable, and a shielding fixture.

[0008] The PCB capacitance probe has a multi-layer PCB structure. Its working surface is provided with a measuring electrode, a protective electrode surrounding the measuring electrode, and a shielding electrode located outside the protective electrode. The non-working surface is provided with a bottom shielding electrode pad, a bottom measuring electrode pad, and a bottom protective electrode ring pad surrounding the bottom measuring electrode pad.

[0009] The local Faraday cage is welded to the bottom protective electrode annular pad, extends outward toward the non-working surface of the PCB capacitance probe, and remains insulated from the bottom measuring electrode pad.

[0010] The center core, middle protective layer, and outer shielding layer of the three coaxial cable are electrically connected to the measuring end, protective end, and shielding end of the PCB capacitance probe, respectively.

[0011] The shielding fixture is mounted on the non-working surface of the PCB capacitor probe and is electrically connected to the shielding electrode or the outer shielding layer of the triaxial cable.

[0012] A second aspect of the present invention discloses an assembly method for the above-mentioned three-coaxial capacitive sensor, comprising the following steps:

[0013] Design the dimensions of the three coaxial electrodes, inner protective copper, blind and buried vias, and bottom pads on the PCB working surface according to the target measurement range;

[0014] The PCB capacitance probe is fabricated using a multilayer PCB process, and the continuity and insulation of the measuring end, protection end, and shielding end are checked. A local Faraday cage is soldered onto the bottom protective electrode annular pad.

[0015] Strip the ends of the three-coaxial cable to expose the center core, middle protective layer and outer shielding layer to a predetermined length, and connect them to the measuring end, protective end and shielding end respectively;

[0016] Position and fix the shielding fixture to the PCB capacitor probe so that the groove avoids the local Faraday cage;

[0017] The assembled sensor is connected to a micro-capacitance detection circuit to perform basic capacitance, displacement response, and noise tests.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) By using PCB technology to form measurement, protection and shielding electrodes, the processing cost and iteration cycle of traditional mechanical processing of three coaxial probes can be reduced, and the consistency of small batch prototypes can be improved.

[0020] (2) By using the annular protective electrode on the working surface and the inner protective copper layer, the measuring electrode and its traces are kept in the equipotential protection area as much as possible, which can suppress the edge effect of the measuring electrode and the parasitic capacitance of the traces in the board.

[0021] (3) The measurement end is brought out by blind buried hole, and the measurement trace is surrounded by inner protective copper layer and bottom protective copper layer, which can reduce the parasitic capacitance caused by the trace and via in the PCB board.

[0022] Simulation results show that when using a conventional through-hole lead-out structure, there is significant interlayer parasitic coupling between the measuring end and the underlying copper layer, resulting in an initial measured capacitance of approximately 93.74 fF. This large initial measured capacitance is unstable and can overwhelm minute capacitance changes caused by the measured displacement, reducing the sensor's measurement resolution and stability. To reduce the impact of interlayer parasitic coupling on displacement sensing, this invention employs a blind buried via lead-out structure and incorporates a double-layer protective copper electrode in the working area. After optimization, the sensor's initial measured capacitance is reduced to approximately 0.03 fF. Within the local working range, the measured capacitance and displacement exhibit an approximately linear relationship, with a sensitivity of approximately 2.85 fF / mm and a nonlinearity of approximately 0.58%.

[0023] (4) By using the bottom protective electrode ring pad and the local Faraday cage, the bottom measuring electrode pad and the exposed section of the center core of the triaxial cable are surrounded by the protective potential, reducing the parasitic coupling between the measuring end and the shielding end.

[0024] Maxwell electric field simulation results show that when using exposed pin headers, there is significant electric field leakage and electric field concentration in the pin header area; after using a local Faraday cage and bottom protective electrode ring pad, the measurement end pad and the exposed section of the center core wire are surrounded by a protective potential, and the electric field leakage outside the connection area is significantly reduced.

[0025] (5) By connecting the three terminals of the PCB capacitance probe to the three coaxial cables, the potential relationship between the measuring end, the protection end and the shielding end can be continuously extended to the external detection circuit, thereby improving the stability of the acquisition of small capacitance signals.

[0026] (6) By setting up a shielding fastener with a groove, the local Faraday cage can obtain assembly clearance space, while the external fixed structure can undertake the functions of shielding and mechanical support, taking into account electrical performance, mechanical reliability and machinability. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the three coaxial electrodes on the working surface of the PCB capacitor probe in this embodiment of the application;

[0028] Figure 2 This is a schematic diagram of the interlayer structure of the PCB capacitance probe and the protection relationship of the measurement traces in the embodiments of this application;

[0029] Figure 3 This is a schematic diagram of the bottom partial Faraday cage and the connection of the three coaxial cables in an embodiment of this application;

[0030] Figure 4 This is a schematic diagram of the shielding fastener structure in an embodiment of this application;

[0031] Figure 5 This is a schematic diagram of the processing and assembly of an embodiment of this application;

[0032] Figure 6 This is a diagram showing the installation of a three-coaxial capacitive sensor according to an embodiment of this application;

[0033] Figure 7 This is a comparison chart of simulation results for Experiment 1 of the embodiments of this application;

[0034] Figure 8 This is a comparison chart of simulation results for Experiment 2 of the embodiments of this application;

[0035] Figure 9 This is a comparison chart of simulation results for Experiment 3 of the present application.

[0036] Explanation of reference numerals in the attached diagram: 1. Measuring electrode; 2. Protective electrode; 3. Shielding electrode; 4. PCB capacitance probe; 5. Protective copper layer; 6. Blind or buried via; 7. Measuring trace; 8. Bottom measuring electrode pad; 9. Bottom protective electrode ring pad; 10. Bottom shielding electrode pad; 11. Local Faraday cage; 12. Triaxial cable; 13. Groove; 14. Positioning protrusion; 15. Shielding fastener; 16. Positioning hole; 17. Screw hole. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the present invention will be further described below with reference to the accompanying drawings. It should be understood that the following embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection. Without departing from the core idea of ​​the embodiments of the present invention, the electrode shape, the number of layers, the via form, the shape of the fixing component, and the specific processing method of the local Faraday cage can all be adjusted according to the actual processing conditions.

[0038] This application provides a triaxial capacitive sensor based on a printed PCB, including: a PCB capacitive probe, a partial Faraday cage, a triaxial cable, and a shielding fixture.

[0039] The PCB capacitance probe has a multi-layer PCB structure. Its working surface is provided with a measuring electrode, a protective electrode surrounding the measuring electrode, and a shielding electrode located outside the protective electrode. The non-working surface is provided with a bottom shielding electrode pad, a bottom measuring electrode pad, and a bottom protective electrode ring pad surrounding the bottom measuring electrode pad.

[0040] The measuring electrode is a circular electrode, the protective electrode is a ring electrode, and the shielding electrode is a conductive area surrounding the outer side of the protective electrode, the shape of which is adapted to the outer contour of the PCB capacitance probe; the measuring electrode, the protective electrode, and the shielding electrode are arranged concentrically or in a ring around the working surface of the PCB capacitance probe.

[0041] The local Faraday cage is welded to the bottom protective electrode annular pad, extends outward toward the non-working surface of the PCB capacitance probe, and remains insulated from the bottom measuring electrode pad.

[0042] The center core, middle protective layer, and outer shielding layer of the three coaxial cable are electrically connected to the measuring end, protective end, and shielding end of the PCB capacitance probe, respectively.

[0043] The shielding fixture is mounted on the non-working surface of the PCB capacitor probe and is electrically connected to the shielding electrode or the outer shielding layer of the triaxial cable.

[0044] Furthermore, at least one inner layer of the PCB capacitor probe is provided with a protective copper layer that is electrically connected to the protective electrode.

[0045] Furthermore, the measurement electrode is connected to the measurement trace inside the PCB via a blind / buried via, and the measurement trace is then connected to the bottom measurement electrode pad via a blind / buried via. The measurement trace is surrounded in the PCB thickness direction by the protection potential region corresponding to the bottom protection electrode annular pad.

[0046] Furthermore, the bottom shielding electrode pad is electrically connected to the shielding electrode through a via provided on the top layer of the PCB capacitor probe.

[0047] Furthermore, the center core wire of the triaxial cable is soldered to the bottom measuring electrode pad, the middle protective layer is electrically connected to the bottom protective electrode annular pad, the protective copper layer or the local Faraday cage, and the outer shielding layer is electrically connected to the bottom shielding electrode pad, the shielding electrode or the shielding fastener.

[0048] Furthermore, the exposed section of the center core wire of the triaxial cable is located within the area surrounded by the bottom protective electrode annular pad.

[0049] Furthermore, the shielding fixture is a conductive metal component with a groove for avoiding the local Faraday cage. An insulating gap is maintained between the local Faraday cage and the shielding fixture, ensuring that the measuring electrode, protective electrode, and shielding electrode form a continuous and shielded triaxial potential structure from the PCB capacitance probe to the triaxial cable. The groove is sized to create an insulating gap between the shielding fixture and the local Faraday cage, preventing short circuits between the protective and shielding ends.

[0050] Specifically, the shielding fastener may also be provided with positioning protrusions, positioning hole mating structures, screw holes, countersunk holes or mounting planes for mating with PCB capacitor probes and external mounting structures.

[0051] Furthermore, the measurement electrode is connected to the measurement trace inside the PCB through a blind via. The measurement trace is surrounded or isolated in the PCB thickness direction by the protective copper layer or the protective potential area corresponding to the bottom protective electrode ring pad, thereby reducing the direct parasitic coupling between the measurement trace and the shielding electrode, fixing components or external conductors.

[0052] like Figure 6 As shown, based on the same concept as the above embodiments, this embodiment adopts a four-layer PCB capacitance probe, providing a specific assembly structure for the aforementioned sensor, including: measuring electrode 1, protective electrode 2, shielding electrode 3, PCB capacitance probe 4, protective copper layer 5, blind via 6, measuring trace 7, bottom measuring electrode pad 8, bottom protective electrode annular pad 9, bottom shielding electrode pad 10, local Faraday cage 11, triaxial cable 12, groove 13, positioning protrusion 14, shielding fastener 15, positioning hole 16, and screw hole 17. The following is a detailed description of each component:

[0053] like Figure 1 As shown, the working surface of the PCB capacitance probe 4 is provided with a central measuring electrode 1, an equipotential protection electrode 2 surrounding the central measuring electrode 1, and a shielding electrode 3 located outside the protection electrode 2; an insulating gap is left between the measuring electrode 1 and the protection electrode 2, and between the protection electrode 2 and the shielding electrode 3.

[0054] The measuring electrode 1 is connected to the measurement input terminal of the micro-capacitance detection circuit, and the shielding electrode 3 is connected to the shielding terminal or reference ground. The measuring electrode 1 and the shielding electrode 3 serve as the measuring terminal and reference terminal for capacitance detection, respectively, and the equivalent capacitance between them serves as the capacitance to be measured. When the distance between the object being measured and the working surface of the sensor changes, the electric field distribution between the measuring electrode 1 and the shielding electrode 3 changes accordingly, thereby causing a change in the capacitance to be measured. The protection electrode 2 is connected to the equipotential protection drive terminal, making its potential follow that of the measuring electrode 1, thereby reducing the electric field divergence caused by the edge effect of the measuring electrode.

[0055] like Figure 2 As shown, the PCB capacitance probe 4 adopts a four-layer structure, from top to bottom as follows: the first layer is the working electrode layer, the second layer is the protective copper layer, the third layer is the measurement electrode trace layer, and the fourth layer is the bottom pad layer and the bottom protective copper layer. Specifically, the second layer contains the protective copper layer 5, the third layer contains the measurement traces 7, and the fourth layer contains the protective copper layer 5, the bottom measurement electrode pads 8, the bottom protective electrode annular pads 9, and the bottom shielding electrode pads 10.

[0056] The measurement electrode 1 can be connected to the third layer measurement trace 7 through a blind via 6, and the measurement trace 7 is then connected to the bottom measurement electrode pad 8 through a blind via 6. The second layer protective copper layer and the fourth layer bottom protective copper layer are electrically connected through blind via 6, and are also electrically connected to the bottom protective electrode annular pad 9, so that the measurement trace 7 is surrounded or isolated by the protective electrode area in the PCB thickness direction.

[0057] like Figure 3 As shown in (b), the non-working surface of the PCB capacitance probe 4 is provided with a bottom measuring electrode pad 8, a bottom protective electrode ring pad 9 arranged around the bottom measuring electrode pad 8, and a shielding electrode pad 10 connected to the shielding end.

[0058] like Figure 3 As shown in (a), a local Faraday cage 11 is soldered onto the bottom protective electrode annular pad 9. The local Faraday cage 11 can be composed of a metal ring, a copper foil cover, a metal sleeve, or a custom-made small protective cover, and extends outward toward the non-working surface of the PCB capacitance probe 4. The local Faraday cage 11 is insulated from the bottom measuring electrode pad 8 and is used to surround the connection area between the bottom measuring electrode pad and the center core of the triaxial cable, thereby forming an equipotential protection space around the measuring solder joint.

[0059] The central core of the triaxial cable 12 is soldered to the bottom measuring electrode pad 8, the intermediate protective layer is connected to the bottom protective electrode annular pad 9, the protective copper layer 5, or the partial Faraday cage 11, and the outer shielding layer is connected to the bottom shielding electrode pad 10, the shielding electrode 3, or the shielding fixing component 15. Thus, the central core, intermediate protective layer, and outer shielding layer of the triaxial cable correspond one-to-one with the measuring end, protective end, and shielding end of the PCB capacitance probe.

[0060] It is worth noting that the exposed length of the center core wire should be minimized during assembly to ensure that the exposed section is within the protection potential range.

[0061] like Figure 4 As shown, the shielding fastener 15 is preferably a machined metal part, made of aluminum alloy, stainless steel, copper alloy, or other conductive materials. This fastener has screw holes 17, grooves 13, and positioning protrusions 14 for positioning and assembly with the external mounting bracket and the PCB capacitance probe. The grooves 13 avoid the partial Faraday cage 11, ensuring insulation between the partial Faraday cage 11 and the shielding fastener 15. The positioning protrusions 14 correspond to the two positioning holes 16 on the PCB capacitance probe 4 and are insulated from non-target electrodes on the PCB or only connected to the predetermined shielding end to avoid short-circuiting the measuring or protective ends.

[0062] During assembly, the positioning protrusion 14 is inserted into the positioning hole 16 to achieve relative positioning between the PCB capacitor probe 4 and the shielding fastener 15. The shielding fastener 15 can be connected to the bottom shielding electrode pad 10 or the outer shielding layer of the triaxial cable 12 through conductive connection, and is mechanically fixed to the PCB capacitor probe 4 through non-conductive adhesive, positioning protrusion 14, positioning hole 16 and screw hole 17.

[0063] In summary, this embodiment of the application achieves layered arrangement of the measuring end, protection end, and shielding end through a multi-layer PCB structure, and combines a bottom partial Faraday cage and shielding fasteners to protect and shield the welding area of ​​the measuring electrodes and the cable connection area. This structure can reduce the influence of connection parasitic capacitance and external interference, while taking into account assembly positioning and mechanical fixation, and is suitable for stable detection of small capacitance signals.

[0064] like Figure 5 As shown in the figure, this application embodiment also provides an assembly method for the above-mentioned three coaxial capacitive sensors, including the following steps:

[0065] Design the dimensions of the three coaxial electrodes, inner protective copper, blind and buried vias, and bottom pads on the PCB working surface according to the target measurement range;

[0066] The PCB capacitance probe is fabricated using a multilayer PCB process, and the continuity and insulation of the measuring end, protection end, and shielding end are checked.

[0067] Weld or fix a local Faraday cage on the bottom protective electrode annular pad;

[0068] Strip the ends of the three coaxial cables to expose appropriate lengths of the center core, middle protective layer, and outer shielding layer, and connect them to the bottom measuring electrode pad, bottom protective electrode ring pad, and bottom shielding electrode pad, respectively.

[0069] Position and fix the shielding fixture to the PCB capacitor probe, ensuring the groove avoids the local Faraday cage;

[0070] The assembled sensor is connected to a micro-capacitance detection circuit to perform basic capacitance, displacement response, and noise tests.

[0071] In one implementation, the local Faraday cage can be first connected to the intermediate protective layer of the triaxial cable and then fixed to the PCB capacitor probe.

[0072] In one embodiment, the shielding fastener can also be fixed by a combination of adhesive and positioning protrusions.

[0073] To further illustrate the technical effects of the above structure, the embodiments of this application also underwent Maxwell simulation verification, including the following three experiments:

[0074] Experiment 1: Compare the electric field distribution with and without a protective electrode to verify the constraint effect of the protective electrode on the electric field at the edge of the measuring electrode.

[0075] Maxwell electric field simulation results show that, without a protective electrode, the electric field at the edge of the measuring electrode diverges significantly outwards. Figure 7 (a) After setting the protective electrode, the electric field at the edge of the measuring electrode is confined to the inside of the protective electrode, and the electric field in the non-target area on the outside is significantly weakened, see [reference needed]. Figure 7 (b) This demonstrates that the protective electrode provided in this application can mitigate the impact of edge effects on the measured capacitance.

[0076] Experiment 2: Compare the capacitance value change curves of ordinary through-hole lead-out structures and blind / buried via protected lead-out structures to verify the suppression effect of blind / buried vias and protective copper layer surrounding structures on parasitic capacitance of traces within the board.

[0077] like Figure 8 As shown in (a), when using a conventional through-hole lead-out structure, significant interlayer parasitic coupling is formed between the measuring end and the underlying copper layer. The initial capacitance to be measured is approximately 93.74 fF. This large initial capacitance is not conducive to the capacitance sensor detecting minute capacitance changes. Figure 8As shown in Figure (b), after adopting the blind via and double-layer protective copper electrode structure, the initial capacitance to be measured is approximately 0.03 fF, and the capacitance to be measured and the displacement show an approximately linear relationship within the local working range. This demonstrates that the blind via and double-layer protective copper surround structure can reduce non-target coupling during the measurement end's lead-out process inside the PCB, effectively reducing the impact of the initial capacitance to be measured on the sensor's detection performance.

[0078] Experiment 3: Compare the electric field distribution of the exposed pin header connection structure and the local Faraday cage protection structure to verify the suppression effect of the bottom protective electrode ring pad and the local Faraday cage on parasitic coupling at the connection end.

[0079] like Figure 9 As shown in (a), in the simulation of the connection end, obvious electric field leakage occurs near the exposed pin header. However, after using a local Faraday cage, the bottom measuring solder joint and the exposed section of the center core wire are surrounded by the protective potential, and the electric field leakage on the outside of the connection end is significantly reduced. Figure 9 (b)

[0080] The simulation results above show that this application can suppress the edge effect of the measurement electrode, reduce the parasitic capacitance of the in-board traces, and reduce the parasitic coupling at the connection end.

[0081] Obviously, the above embodiments are merely examples to clearly illustrate the present invention and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description, and all obvious variations or modifications derived from the inventive technical solution are still within the scope of the claims of the present invention.

Claims

1. A triaxial capacitive sensor based on a printed PCB, characterized in that, include: PCB capacitance probe, local Faraday cage, triaxial cable and shielding fixture; The PCB capacitance probe has a multi-layer PCB structure. Its working surface is provided with a measuring electrode, a protective electrode surrounding the measuring electrode, and a shielding electrode located outside the protective electrode. The non-working surface is provided with a bottom shielding electrode pad, a bottom measuring electrode pad, and a bottom protective electrode ring pad surrounding the bottom measuring electrode pad. The local Faraday cage is welded to the bottom protective electrode annular pad, extends outward toward the non-working surface of the PCB capacitance probe and remains insulated from the bottom measuring electrode pad; The center core, middle protective layer, and outer shielding layer of the three coaxial cable are electrically connected to the measuring end, protective end, and shielding end of the PCB capacitance probe, respectively. The shielding fixture is mounted on the non-working surface of the PCB capacitor probe and is electrically connected to the shielding electrode or the outer shielding layer of the triaxial cable.

2. A triaxial capacitive sensor based on a printed PCB according to claim 1, characterized in that, At least one inner layer of the PCB capacitor probe is provided with a protective copper layer that is electrically connected to the protective electrode.

3. A triaxial capacitive sensor based on a printed PCB according to claim 2, characterized in that, The measurement electrode is connected to the measurement trace inside the PCB through a blind via, and the measurement trace is then connected to the bottom measurement electrode pad through a blind via.

4. A triaxial capacitive sensor based on a printed PCB according to claim 3, characterized in that, The measurement trace is surrounded by the protection potential area corresponding to the bottom protection electrode annular pad in the PCB thickness direction.

5. A triaxial capacitive sensor based on a printed PCB according to any one of claims 1-4, characterized in that, The bottom shielding electrode pad is electrically connected to the shielding electrode through a via located on the top layer of the PCB capacitor probe.

6. A triaxial capacitive sensor based on a printed PCB according to claim 2, characterized in that, The center core of the three coaxial cables is soldered to the bottom measuring electrode pad, the middle protective layer is electrically connected to the bottom protective electrode ring pad, the protective copper layer or the local Faraday cage, and the outer shielding layer is electrically connected to the bottom shielding electrode pad, the shielding electrode or the shielding fastener.

7. A triaxial capacitive sensor based on a printed PCB according to claim 6, characterized in that, The exposed section of the center core of the triaxial cable is located within the area surrounded by the bottom protective electrode annular pad.

8. A triaxial capacitive sensor based on a printed PCB according to claim 1, characterized in that, The shielding fixture has a groove for avoiding the local Faraday cage, and an insulating gap is maintained between the local Faraday cage and the shielding fixture, so that the measuring electrode, the protective electrode and the shielding electrode form a continuous and shielded triaxial potential structure from the PCB capacitance probe to the triaxial cable.

9. A triaxial capacitive sensor based on a printed PCB according to claim 1 or 8, characterized in that, The shielding fastener is a conductive metal component.

10. A method for assembling the triaxial capacitive sensor according to any one of claims 1-9, characterized in that, Includes the following steps: Design the dimensions of the three coaxial electrodes, inner protective copper, blind and buried vias, and bottom pads on the PCB working surface according to the target measurement range; The PCB capacitance probe is fabricated using a multilayer PCB process, and the continuity and insulation of the measuring end, protection end, and shielding end are checked. A local Faraday cage is soldered onto the bottom protective electrode annular pad. Strip the ends of the three-coaxial cable to expose the center core, middle protective layer and outer shielding layer to a predetermined length, and connect them to the measuring end, protective end and shielding end respectively; Position and fix the shielding fixture to the PCB capacitor probe so that the groove avoids the local Faraday cage; The assembled sensor is connected to a micro-capacitance detection circuit to perform basic capacitance, displacement response, and noise tests.

Images