Linear displacement sensor with notch low-pass filtering response and manufacturing method and displacement measuring method thereof

Abstract

The invention discloses a linear displacement sensor with notch low-pass filtering response. The linear displacement sensor comprises a lower-layer dielectric plate, an upper-layer dielectric plate and an upper-layer embedded dielectric plate which are stacked from bottom to top, the top surface of the lower dielectric plate is provided with a microstrip transmission line, and one side of the microstrip transmission line is provided with a plurality of periodically arranged periodic branches. Two ends of the microstrip transmission line are respectively connected to the input port and the output port; a rectangular through hole is formed in the middle of the upper dielectric plate; the upper layer embedded dielectric plate is configured in the rectangular through hole; a resonator is arranged on the surface of the bottom of the upper embedded dielectric plate, forms non-contact electromagnetic coupling with the microstrip transmission line through a coupling microstrip line segment, and is used for generating a notch frequency in a passband of the low-pass filter; on the premise of keeping the notch frequency constant, the electrical length between the resonator and the input port is changed, so that the reflection phase at the notch frequency of the input port is linearly changed along with the displacement distance.

Description

Technical Field

[0001] This application relates to the fields of microwave sensing technology and filter technology, specifically to a linear displacement sensor that integrates low-pass filtering function with displacement sensing function. Background Technology

[0002] Linear displacement sensors are widely used in industrial automation, precision measurement, and robot positioning. Traditional displacement sensors include types such as optical encoders, magnetic encoders, inductive sensors, and capacitive sensors. These sensors have certain limitations in specific application scenarios. While optical encoders offer high accuracy, they are susceptible to contamination and vibration. Magnetic encoders are sensitive to electromagnetic interference. Inductive and capacitive sensors have limited measurement ranges and insufficient anti-interference capabilities in high-frequency electromagnetic environments.

[0003] Microwave sensors have gained increasing attention due to their advantages such as non-contact measurement, strong resistance to electromagnetic interference, and fast measurement speed. Existing microwave displacement sensors mainly operate based on the principle of resonant frequency shift or phase measurement. Sensors based on resonant frequency shift measure displacement by detecting changes in the resonator frequency with displacement; however, frequency measurement sensitivity is typically low, and the need for wideband scanning increases measurement time. While phase measurement-based sensors can achieve higher sensitivity, existing solutions often employ single-function designs, lacking built-in filtering capabilities. This makes them susceptible to external interference signals in complex electromagnetic environments, requiring external filters for proper operation. This results in a complex system structure, increased size, and higher cost.

[0004] Furthermore, existing microwave displacement sensors often struggle to maintain stable electromagnetic characteristics throughout the measurement process. When the sensing structure moves, its coupling relationship with the signal transmission line may change, leading to inconsistent measurement sensitivity or introducing nonlinear errors, thus affecting measurement accuracy and repeatability. How to achieve high-sensitivity displacement measurement while maintaining stable filtering characteristics and electromagnetic coupling is a critical technical problem that needs to be solved by current technologies.

[0005] Therefore, there is an urgent need for a linear displacement sensor that integrates filtering functions, has high linearity and high sensitivity, and maintains stable electromagnetic characteristics throughout the measurement range, in order to meet the high-precision displacement measurement requirements in complex electromagnetic environments. Summary of the Invention

[0006] This invention aims to solve the technical problems of existing microwave displacement sensors, such as limited functionality, lack of built-in filtering capability, insufficient sensitivity and linearity, and unstable electromagnetic characteristics during measurement. It provides a linear displacement sensor that integrates a notch low-pass filter response, has high linearity and high sensitivity, and maintains stable filtering characteristics and electromagnetic coupling relationship throughout the entire measurement range.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A linear displacement sensor with a notch low-pass filter response includes a lower dielectric substrate, an upper dielectric substrate, and an upper embedded dielectric substrate stacked from bottom to top.

[0008] The bottom surface of the lower dielectric substrate is provided with a metal grounding plate, and the top surface is provided with a microstrip transmission line extending along a first direction. One side of the microstrip transmission line is provided with multiple periodically arranged periodic branches, which together form a low-pass filter. The two ends of the microstrip transmission line are respectively connected to an input port and an output port.

[0009] The upper dielectric plate is a pure dielectric layer, with a rectangular through hole penetrating its thickness in its middle.

[0010] The upper embedded dielectric substrate is disposed within the rectangular through-hole and is limited to linear sliding only along the first direction. A resonator is disposed on the bottom surface of the upper embedded dielectric substrate. The resonator forms a non-contact electromagnetic coupling with the microstrip transmission line through a coupled microstrip line segment, which is used to generate a notch frequency in the passband of the low-pass filter.

[0011] The linear sliding of the upper embedded dielectric substrate changes the electrical length between the resonator and the input port while keeping the notch frequency constant, thereby causing the reflection phase of the input port at the notch frequency to change linearly with the displacement distance.

[0012] This invention provides a method for manufacturing a linear displacement sensor, characterized by comprising the following steps: a) Forming microstrip transmission lines and periodic stubs on the top surface of the lower dielectric substrate). b) Form a rectangular through-hole in the middle of the upper dielectric substrate; c) Form a resonator and a coupled microstrip line segment on the bottom surface of the upper embedded dielectric substrate; d) Align and stack the upper dielectric substrate and bond it to the top of the lower dielectric substrate; e) The upper embedded medium plate is installed in the rectangular through hole to form a stable non-contact electromagnetic coupling.

[0013] This invention provides a displacement measurement method using a linear displacement sensor, characterized by comprising the following steps: a) Feed a microwave signal with a frequency equal to the notch frequency into the input port of the sensor; b) When the upper embedded medium board is displaced, the reflection phase of the input port is measured in real time; c) Calculate the displacement distance based on the change in the reflection phase and a preset linear sensitivity coefficient. Attached Figure Description

[0014] Figure 1 This is a three-dimensional structural schematic diagram of a linear displacement sensor with a notched low-pass filter response according to an embodiment of the present invention.

[0015] Figure 2 This is a top view schematic diagram of a linear displacement sensor with a notched low-pass filter response according to an embodiment of the present invention.

[0016] Figure 3 This is a frequency response curve of the transmission coefficient S21 of a linear displacement sensor with a notched low-pass filter response at different displacement positions according to an embodiment of the present invention.

[0017] Figure 4 This is a graph showing the relationship between the reflection phase and frequency at the input port of a linear displacement sensor with a notched low-pass filter response at different displacement positions, according to an embodiment of the present invention.

[0018] Figure 5 This is a graph showing the linear relationship between the input port reflection phase and displacement distance of a linear displacement sensor with a notched low-pass filter response in one embodiment of the present invention at the notched frequency.

[0019] In the diagram: 10. Lower layer filter structure; 11. Lower layer dielectric substrate; 111. Metal ground plane; 112. Microstrip transmission line; 113. Periodic stub; 12. Input port; 13. Output port; 20. Upper layer support structure; 21. Upper layer dielectric substrate; 211. Rectangular via; 30. Upper layer embedded movable sensing structure; 31. Upper layer embedded dielectric substrate; 32. Coupled microstrip line segment; 33. Square ring resonator; 41. Adhesive layer; 42. Guiding mechanism. Detailed Implementation

[0020] The present application will be further described below with reference to specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0021] In the description of this application, it should be noted that the terms "center", "lateral", "longitudinal", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., which indicate the orientation and positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and 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, and should not be construed as limiting the specific protection scope of this application.

[0022] It should be noted that the terms "first," "second," etc., in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0023] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or device.

[0024] See Figures 1 to 5 As shown, this embodiment discloses a linear displacement sensor with a notch low-pass filter response. The linear displacement sensor adopts a three-layer dielectric structure stacked from bottom to top, including a lower filter structure 10, an upper support structure 20, and an upper embedded movable sensing structure 30. The lower-layer filter structure 10 constitutes a low-pass filter with periodic branches. A square ring resonator 33 is set at the bottom of the upper-layer embedded movable sensing structure 30. The square ring resonator 33 generates a notch response with a fixed frequency in the passband of the low-pass filter through a non-contact electromagnetic coupling method. When the upper-layer embedded movable sensing structure 30 slides linearly along the extension direction of the microstrip transmission line, it changes the electrical length between the square ring resonator 33 and the input port 12, so that the reflection phase of the input port 12 at the notch frequency changes linearly with the displacement distance. This realizes the integrated integration of filtering function and displacement sensing function. Compared with the existing microwave displacement sensors that require external filters, the system integration is significantly improved, the overall volume is reduced by about 40%, and the filtering response characteristics are maintained throughout the entire sliding stroke. The filter cutoff frequency fluctuation is less than 1%, and the notch depth change is less than 1dB. This provides a reliable technical means for high-precision displacement measurement in complex electromagnetic environments.

[0025] See Figure 1As shown, the lower-layer filter structure 10 includes a lower dielectric substrate 11, which is made of a low-loss microwave dielectric material. The relative permittivity of this low-loss microwave dielectric material ranges from 2.2 to 10.2, the loss tangent is less than 0.01, and the thickness ranges from 0.5 mm to 3 mm. Optional materials include Rogers RO4003C series, FR4 high-frequency board, polytetrafluoroethylene composite material, ceramic-filled composite material, or foam dielectric material, etc., all of which meet the requirements for microwave transmission performance. A metal ground plane 111 is attached to the bottom surface of the lower dielectric substrate 11. This metal ground plane 111 is made of conductive metal foil, preferably copper foil, aluminum foil, or silver foil, with a thickness ranging from 18 μm to 70 μm, covering the entire bottom of the dielectric substrate. It provides a reference ground plane for the microstrip transmission line and achieves electromagnetic shielding. A microstrip transmission line 112 is disposed on the top surface of the lower dielectric substrate 11. This microstrip transmission line 112 is designed with a characteristic impedance of 50 ohms. The thickness of the conductive metal material ranges from 18 μm to 70 μm. The linewidth is determined by the relative permittivity and thickness of the dielectric substrate using the microstrip line impedance calculation formula, ranging from 0.5 mm to 5 mm. It extends along a first direction, defined as the first axis, with a total length ranging from 100 mm to 300 mm. The left end of the microstrip transmission line 112 is connected to the input port 12, and the right end is connected to the output port 13. Both the input port 12 and the output port 13 use RF connectors with a characteristic impedance of 50 ohms, with selectable types being SMA connectors, N-type connectors, or K-type connectors, for establishing RF signal connections with external measurement equipment. One side of the microstrip transmission line 112, defined as the positive direction of the second axis, is periodically arranged with multiple periodic branches 113. The number of these periodic branches 113 ranges from 11 to 25. Each branch 113 is perpendicular to the microstrip transmission line 112 and extends along the positive direction of the second axis, directly connecting to the edge of the microstrip transmission line 112 without gaps. The branch width ranges from 0.2 mm to 2 mm, the thickness of the conductive metal material ranges from 18 μm to 70 μm, the center-to-center spacing of the branches in the first axis direction ranges from 2 mm to 10 mm, and the total length of the branches in the first axis direction ranges from 40 mm to 150 mm, located in the central region of the microstrip transmission line 112. The lengths of the multiple branches 113 are symmetrically and gradually distributed, with the longest branch at the center ranging from 5 mm to 15 mm. The lengths of the branches decrease gradually from the center to both sides at intervals of 0.3 mm to 2 mm, and the shortest branches at both ends range from 0.5 mm to 3 mm.The periodic stub structure 113, acting as a distributed capacitive load, forms an LC low-pass filter network with the inductive characteristics of the microstrip transmission line 112. The symmetrically varied distribution of stub lengths achieves a Chebyshev-like or Butterworth-like filter response, thereby achieving low-pass filter characteristics with a passband flatness better than 1.5dB, an adjustable cutoff frequency range of 2GHz to 8GHz, and a stopband suppression greater than 20dB. Compared with traditional lumped-parameter LC low-pass filters, this artificial surface plasmon polariton structure filter maintains low-pass characteristics while having a more compact physical size, reducing the overall length by about 30% to 60%, and avoiding parasitic effects and reliability issues introduced by lumped element welding.

[0026] See Figure 1 and Figure 2 As shown, the upper support structure 20 includes an upper dielectric plate 21, which is also made of a low-loss microwave dielectric material. The relative permittivity of the low-loss microwave dielectric material ranges from 2.2 to 10.2, the loss tangent is less than 0.01, and the thickness ranges from 0.5 mm to 3 mm. The optional materials are Rogers RO4003C series, FR4 high-frequency board, polytetrafluoroethylene composite material, ceramic-filled composite material, or foam dielectric material. There are no metal covering layers at the top and bottom, making it a pure dielectric structure. A rectangular through-hole 211 is provided in the central region of the upper dielectric substrate 21. This rectangular through-hole 211 completely penetrates the dielectric substrate from the top surface to the bottom surface. The length of the through-hole ranges from 60mm to 150mm along the first axis, and the width ranges from 10mm to 40mm along the second axis. The center line of the through-hole is aligned with the center line of the microstrip transmission line 112 on the horizontal plane projection. The through-hole covers the entire distribution area of ​​the periodic branches 113 along the first axis and leaves a margin of 5mm to 20mm at each end. The through-hole extends 5mm to 20mm to each side of the second axis. This rectangular through-hole 211 provides precise sliding guide space for the upper embedded dielectric substrate 31. By controlling the fit clearance between the through-hole and the embedded dielectric substrate, it is ensured that the embedded dielectric substrate 31 moves only along the first axis during sliding. The positional deviations in the second axis and Z-axis directions are strictly limited, thereby achieving a highly stable electromagnetic coupling relationship and ensuring the consistency of the sensor's filtering response throughout the entire measurement range.

[0027] See Figure 1 and Figure 2As shown, the upper embedded movable sensing structure 30 includes an upper embedded dielectric substrate 31, a coupled microstrip line segment 32, and a square ring resonator 33. The upper embedded dielectric substrate 31 is made of a low-loss microwave dielectric material with a relative permittivity ranging from 2.2 to 10.2, a loss tangent of less than 0.01, and a thickness ranging from 0.5 mm to 3 mm. Optional materials include Rogers RO4003C series, FR4 high-frequency board, polytetrafluoroethylene composite material, ceramic-filled composite material, or foam dielectric material. Its external dimensions range from 55 mm to 145 mm in length along the first axis and from 8 mm to 38 mm along the second axis, being 0.5 mm to 2 mm smaller than the dimensions of the rectangular through-hole 211 in all directions, forming a mating clearance of 0.25 mm to 1 mm. The upper embedded dielectric plate 31 is embedded inside a rectangular through-hole 211. Sliding guidance is achieved through guide mechanisms 42 installed on the inner walls of both sides of the rectangular through-hole 211. These guide mechanisms 42 can be made of low-friction materials or mechanisms such as polytetrafluoroethylene (PTFE), ultra-high molecular weight polyethylene (UHMWPE), stainless steel slide rails, ceramic guide pillars, or linear ball bearing guides. The guide gap is controlled within the range of 0.3mm to 2mm, ensuring smooth sliding while controlling the variation in the vertical distance between the upper embedded dielectric plate 31 and the lower dielectric plate 11 within ±0.1mm. This achieves high stability of the electromagnetic coupling strength throughout the entire sliding stroke range of 50mm to 150mm, with coupling strength fluctuations less than 5%, thus ensuring the stability of the notch frequency depth and the repeatability of displacement measurements. The top surface of the upper embedded dielectric plate 31 has no metal covering layer, while the bottom surface is provided with a coupling microstrip line segment 32 and a square ring resonator 33. The coupling microstrip segment 32 is made of a conductive metal material with a thickness ranging from 18 μm to 70 μm, preferably copper foil, aluminum foil, or silver foil. The linewidth is designed to be between 0.5 mm and 5 mm according to the characteristic impedance requirements of the dielectric substrate, with a characteristic impedance of 50 ohms. The length ranges from 8 mm to 30 mm. It extends along the first axis and is located in the middle of the upper embedded dielectric substrate 31. The horizontal plane projection of the coupling microstrip segment 32 overlaps with a certain area of ​​the lower microstrip transmission line 112. The vertical distance between the two ranges from 0.5 mm to 3 mm, which is the thickness of the upper dielectric substrate 21. This vertical stacking structure realizes non-contact electromagnetic coupling from the microstrip transmission line 112 to the coupling microstrip segment 32. The coupling coefficient is adjustable from 0.1 to 0.7. The square ring resonator 33 is directly connected to the middle of the coupled microstrip line segment 32. The square ring resonator 33 is made of a conductive metal material with a thickness ranging from 18 μm to 70 μm, preferably copper foil, aluminum foil or silver foil, an outer side length ranging from 10 mm to 40 mm, and a metal line width ranging from 0.3 mm to 2 mm. An opening is provided on one side of the square ring with a width ranging from 0.3 mm to 3 mm. The opening faces the positive direction of the second axis and is consistent with the extension direction of the periodic branch 113.The square ring resonator 33 has a resonant frequency range of 1.5 GHz to 5 GHz, which is within the passband of the low-pass filter. The square ring resonator 33 establishes electromagnetic coupling with the microstrip transmission line 112 through the coupled microstrip line segment 32. When the square ring resonator 33 resonates, it generates a strong reflection effect, forming a gap with a depth of 20 dB to 50 dB at the resonant frequency on the frequency response curve of the transmission coefficient S21 of the low-pass filter. At the same time, the reflection coefficient S11 of the input port 12 is close to 0 dB at the resonant frequency, achieving total reflection. This achieves a composite filter response that introduces a specific frequency gap while maintaining the low-pass filter function. This gap response is used to suppress interference signals near the resonant frequency. At the same time, the reflection phase at the gap frequency is highly sensitive to changes in electrical length, providing highly sensitive measurement parameters for displacement sensing.

[0028] See Figure 1 As shown, the three-layer structure is assembled through precision alignment and bonding processes. The lower dielectric substrate 11 and the upper dielectric substrate 21 are connected by an adhesive layer 41. This adhesive layer 41 can be made of temperature- and moisture-resistant materials such as epoxy resin, acrylic resin, prepreg, polyimide film, or optical adhesive. The thickness of the adhesive layer ranges from 10μm to 100μm, and this thickness has a negligible impact on the electromagnetic field distribution. During the bonding process, precision positioning fixtures are used to ensure that the alignment accuracy of the two dielectric substrates in the horizontal plane is within ±0.2mm, and the interlayer distance accuracy in the Z-axis direction is within ±0.1mm. After bonding, the layers are cured for 0.5 hours to 3 hours within a temperature range of 60°C to 150°C to achieve a permanent interlayer connection. The upper embedded dielectric plate 31 is installed inside the rectangular through hole 211 through the guide mechanism 42. The design of the guide mechanism 42 ensures that the upper embedded dielectric plate 31 can only slide linearly along the first axis direction. The movement in the second axis and Z axis directions is completely restricted. The sliding resistance is controlled to less than 2 Newtons by using a low friction coefficient material. This enables smooth movement within the sliding stroke range of 50mm to 150mm. During the entire sliding process, the vertical distance between the square ring resonator 33 at the bottom of the upper embedded dielectric plate 31 and the lower microstrip transmission line 112 remains constant within the range of 0.5mm to 3mm, with a distance variation of less than ±0.1mm. This ensures the stability of the electromagnetic coupling strength, which is a key technical guarantee for achieving high repeatability displacement measurement.

[0029] The displacement measurement principle of this linear displacement sensor is based on the linear relationship between the reflected phase and the electrical length. When the operating frequency is set to the notch frequency, i.e., the resonant frequency range of the square ring resonator 33 is 1.5 GHz to 5 GHz, the input port 12 feeds a microwave signal to the microstrip transmission line 112. This signal propagates along the microstrip transmission line 112 and establishes electromagnetic coupling with the coupled microstrip segment 32 at the bottom of the upper embedded dielectric substrate 31 through the electromagnetic field radiated upward through the upper dielectric substrate 21. The coupled electromagnetic energy is transferred to the square ring resonator 33. Since the square ring resonator 33 resonates at this resonant frequency, the generated strong reflected signal returns to the microstrip transmission line 112 through the coupling path and is finally transmitted back to the input port 12. At the initial position, i.e., the displacement distance is 0 mm, the center of the square ring resonator 33 is located at a fixed position on the microstrip transmission line 112. At this time, the electrical length between the square ring resonator 33 and the input port 12 is the initial value θ0, and the reflected phase measured by the input port 12 is the initial phase angle S110. When the upper embedded dielectric substrate 31 slides a distance d along the positive direction of the first axis, the square ring resonator 33 moves accordingly, and the physical distance between it and the input port 12 increases by d. Since the propagation constant β of the electromagnetic wave in the microstrip transmission line 112 remains basically constant near the resonant frequency, ranging from 30 radians per meter to 100 radians per meter, depending on the relative permittivity of the dielectric material, the change in electrical length is Δθ, which is equal to β multiplied by d. Correspondingly, the change in the reflection phase of the input port 12 is ΔS11, which is equal to negative 2 times Δθ. The negative sign indicates that the reflection phase decreases when the displacement increases. Thus, a linear relationship between the reflection phase and the displacement distance is established. Experimental tests show that this linear displacement sensor exhibits adjustable sensitivity of 5 to 25 degrees per millimeter (°C / mm) for reflected phase variation with displacement distance within a sliding stroke range of 50 mm to 150 mm. This sensitivity depends on the operating frequency and the choice of dielectric material. Compared to traditional frequency measurement methods, which typically have a sensitivity of several megahertz per millimeter, this translates to a phase sensitivity of approximately 3 to 5 degrees per millimeter, representing a 1 to 5-fold improvement. This enables high-precision measurement with a displacement resolution of 0.01 mm to 0.05 mm. Within the 50 mm to 150 mm sliding stroke range, the total change in reflected phase ranges from 250 to 3750 degrees, exceeding a 360-degree phase period. By employing a phase unwinding algorithm to handle phase jumps, continuous and unambiguous displacement measurement can be achieved throughout the entire measurement range.

[0030] Throughout the sliding measurement process, the filtering response characteristics of this linear displacement sensor remained highly stable. (See also...) Figure 3The frequency response curve of the transmission coefficient S21 shown indicates that, when the upper embedded dielectric substrate 31 is located at different displacement positions, the change in the low-pass filter cutoff frequency is less than 3%, the change in passband insertion loss in the low-frequency band is less than 0.5 dB, the change in notch frequency is less than 0.5%, and the change in notch depth is less than 3 dB. This stability stems from the fact that the square ring resonator 33 remains above the distribution area of ​​the periodic stubs 113 throughout the sliding process. Although the square ring resonator 33 moves along the first axis, the vertical coupling distance between it and the microstrip transmission line 112 remains constant. Furthermore, the resonant characteristics of the square ring resonator 33 are mainly determined by its own geometry and are not affected by changes in position along the first axis. Therefore, the notch frequency and notch depth remain stable throughout the sliding range. This achieves stable anti-interference filtering performance while performing displacement measurement functions. This performance ensures that the sensor can operate reliably in complex electromagnetic environments. Compared with traditional microwave displacement sensors that require external filters, the system complexity is reduced by approximately 20% to 40%, and the overall cost is reduced by approximately 15% to 35%.

[0031] In an optional implementation, to further improve measurement accuracy and anti-interference capability, a two-port differential measurement method can be used. The connection of output port 13 is maintained, while the reflection coefficient S11 of input port 12 and the transmission coefficient S21 of output port 13 relative to input port 12 are measured simultaneously. At the notch frequency, the phase of both reflection coefficient S11 and transmission coefficient S21 is affected by the displacement distance change; the phase difference Δ between the two is calculated. The phase difference Δ is equal to the phase angle of S11 minus the phase angle of S21. Displacement measurement can eliminate the influence of environmental factors such as temperature and humidity on the common-mode error of the two ports. Experimental verification shows that the differential measurement method reduces the temperature coefficient from -0.01°C to -0.02°C per degree Celsius in single-port measurement to -0.003°C to -0.008°C per degree Celsius, improving the measurement accuracy by about 30% to 60%. The displacement measurement error is controlled within ±0.1 mm in the temperature range of -20°C to +60°C.

[0032] In an alternative implementation, a multi-frequency measurement method can be used to expand the measurement range or resolve phase ambiguity issues. In addition to measuring the reflection phase at the main notch frequency, the reflection phase is also measured at other frequency points within the passband of the low-pass filter. By fusing the phase information from multiple frequency points using a least squares algorithm or a Kalman filter algorithm, the phase period ambiguity problem that occurs when the displacement distance exceeds the phase period of a single frequency point can be solved. Alternatively, multiple square ring resonators, circular ring resonators, or other resonators of different shapes and sizes can be simultaneously set at the bottom of the upper embedded dielectric substrate 31. The resonant frequencies of these resonators are designed at different frequency points in the range of 1.5 GHz to 5 GHz and arranged on the same upper embedded dielectric substrate 31 to achieve multi-frequency simultaneous sensing. The size of each resonator is designed according to its resonant frequency. Multiple resonators are staggered along the second axis or connected in series along the first axis to avoid mutual interference. Experimental verification shows that multi-frequency measurement can expand the ambiguity-free measurement range from 50 mm to 150 mm to 200 mm to 500 mm. At the same time, the measurement reliability is improved by multi-frequency data redundancy. Even if a certain frequency point is affected by interference signals, other frequency points can still provide effective displacement information.

[0033] In an optional embodiment, to achieve high-precision position servo control, the linear displacement sensor can be integrated into a closed-loop control system. The reflected phase measured by input port 12 is converted into the current displacement distance d through a pre-calibrated linear relationship. This displacement distance d is compared with the target displacement distance d target value, and the displacement error e is calculated to be equal to the target value d minus d. A proportional-integral-derivative (PID) controller, a fuzzy controller, or a neural network controller generates a control signal based on the displacement error e. This control signal drives a stepper motor, a DC servo motor, a linear motor, or a piezoelectric ceramic driver to adjust the position of the upper embedded dielectric plate 31, making the displacement error e approach zero. This achieves precision displacement closed-loop control based on microwave phase feedback. Experimental verification shows that the positioning accuracy of the closed-loop control system can reach ±0.01mm to ±0.05mm, the response time is less than 50ms to 200ms, and the repeatability is better than ±0.005mm to ±0.02mm. This closed-loop control capability makes the linear displacement sensor not only usable for displacement measurement but also as a position feedback sensor for precision positioning platforms, with broad application prospects in micro-nano fabrication, precision assembly, robot positioning, and other fields.

[0034] The linear displacement sensor is manufactured using standard printed circuit board or thin-film processes, offering excellent mass production capabilities. The lower dielectric substrate 11 is fabricated by coating a copper-clad laminate of low-loss microwave dielectric material with photoresist of a thickness ranging from 3μm to 10μm. The microstrip transmission lines 112 and periodic stubs 113 are patterned through photomask exposure and development. The conductive metal in unprotected areas is etched away using chemical etching solutions such as ferric chloride solution or alkaline etching solutions. The photoresist is removed, and the surface is cleaned. RF connectors are soldered or crimped onto both ends of the microstrip transmission lines 112 to form input ports 12 and output ports 13. The bottom conductive metal is retained as a metal ground plane 111 and requires no further processing. The linewidth and spacing of the microstrip lines and stubs are inspected using a microscope or optical profilometer to ensure errors are within ±50μm to ±100μm. The S-parameters of the low-pass filter are tested using a vector network analyzer to verify that the cutoff frequency is within the design range. The upper dielectric substrate 21 is manufactured using a low-loss microwave dielectric material board without copper cladding. A rectangular through-hole 211 is machined in the center of the dielectric board using CNC milling, laser cutting, or mechanical stamping. The through-hole size is determined according to design requirements, extending through the entire thickness of the dielectric board. The through-hole size is measured using calipers or a coordinate measuring machine to ensure an error within ±0.1mm to ±0.3mm. The edges of the through-hole are inspected to ensure no burrs or cracks. The upper embedded dielectric substrate 31 is manufactured using a low-loss microwave dielectric material laminate with copper cladding on only one side (i.e., copper cladding only on the bottom). Coupled microstrip segments 32 and square ring resonators 33 are fabricated on the bottom using photolithography and chemical etching processes or laser direct writing. The dielectric board is cut to dimensions that match the rectangular through-hole 211 using CNC milling, laser cutting, or wire cutting. The dimensions and opening of the square ring resonator 33 are ensured to have an error within ±50μm to ±100μm. The resonant frequency of the square ring resonator 33 is confirmed to be within the design range with a deviation of less than ±2% to ±5%. The three-layer structure is assembled using precision alignment fixtures for interlayer positioning. Alignment accuracy is ensured by optical alignment marks or mechanical positioning pins. After applying adhesive, it is cured under controlled temperature and pressure conditions. The guide mechanism 42 is installed and the sliding gap is adjusted to the design range. Finally, the overall electrical performance is tested to verify that the filtering response and displacement sensing performance meet the design specifications, thus completing the mass production process of the linear displacement sensor.

[0035] The basic principles, main features, and advantages of this application have been described above. Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely the principles of this application. Various changes and modifications can be made to this application without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claims. The scope of protection claimed by this application is defined by the appended claims and their equivalents.

Claims

1. A linear displacement sensor with a notch low-pass filter response, characterized in that, It includes a lower dielectric substrate (11), an upper dielectric substrate (21), and an upper embedded dielectric substrate (31) stacked from bottom to top; The bottom surface of the lower dielectric substrate (11) is provided with a metal grounding plate (111), and the top surface is provided with a microstrip transmission line (112) extending along a first direction. A plurality of periodically arranged periodic stubs (113) are provided on one side of the microstrip transmission line (112), which together form a low-pass filter. The two ends of the microstrip transmission line (112) are respectively connected to an input port (12) and an output port (13). The upper dielectric plate (21) is a pure dielectric layer, and a rectangular through hole (211) is provided in its middle that penetrates its thickness. The upper embedded dielectric substrate (31) is disposed within the rectangular through-hole (211) and is limited to linear sliding only along the first direction; a square ring resonator (33) is provided on the bottom surface of the upper embedded dielectric substrate (31), and the square ring resonator (33) forms a non-contact electromagnetic coupling with the microstrip transmission line (112) through a coupled microstrip line segment (32) to generate a notch frequency in the passband of the low-pass filter; The linear sliding of the upper embedded dielectric plate (31) changes the electrical length between the resonator (33) and the input port (12) while keeping the notch frequency constant, so that the reflection phase of the input port (12) at the notch frequency changes linearly with the displacement distance.

2. The linear displacement sensor according to claim 1, characterized in that, The number of the plurality of periodic branches (113) is 11 to 25, and their length distribution is such that the branch located in the middle is the longest, and decreases symmetrically from the central branch to both sides in the first direction.

3. The linear displacement sensor according to claim 2, characterized in that, The length of the central branch is in the range of 5mm to 15mm, the length difference between adjacent branches is in the range of 0.3mm to 2mm, and the length of the branches at both ends is in the range of 0.5mm to 3mm.

4. The linear displacement sensor according to claim 1, characterized in that, The square ring resonator (33) is a ring resonator with an opening, the geometry of which is configured to set the gap frequency in the range of 1.5 GHz to 5 GHz and generate a transmission gap with a depth greater than 20 dB at that frequency.

5. The linear displacement sensor according to claim 1, characterized in that, A guide mechanism (42) is provided between the inner wall of the rectangular through hole (211) and the upper embedded medium plate (31), forming a sliding gap in the range of 0.3mm to 2mm. The guide mechanism (42) is used to control the change in the vertical distance between the upper embedded medium plate (31) and the lower medium plate (11) within ±0.1mm during the sliding process, so as to ensure the stability of the electromagnetic coupling strength.

6. The linear displacement sensor according to claim 1, characterized in that, The lower dielectric substrate (11), the upper dielectric substrate (21), and the upper embedded dielectric substrate (31) are all made of low-loss microwave dielectric material with a relative permittivity in the range of 2.2 to 10.2 and a thickness in the range of 0.5 mm to 3 mm. The overall structure is configured such that the cutoff frequency fluctuation of the low-pass filter is less than 3% and the depth change of the notch frequency is less than 3 dB throughout the entire sliding stroke.

7. A method for manufacturing a linear displacement sensor as described in any one of claims 1 to 6, characterized in that, Includes the following steps: a) A microstrip transmission line (112) and periodic stubs (113) are formed on the top surface of the lower dielectric substrate (11). b) A rectangular through hole (211) is formed in the middle of the upper dielectric plate (21); c) A resonator (33) and a coupled microstrip line segment (32) are formed on the bottom surface of the upper embedded dielectric substrate (31). d) Align and stack the upper dielectric plate (21) and bond it to the top of the lower dielectric plate (11); e) The upper embedded medium plate (31) is installed in the rectangular through hole (211) to form a stable non-contact electromagnetic coupling.

8. The manufacturing method according to claim 7, characterized in that, The bonding and fixing step uses a precision positioning jig to ensure alignment accuracy within ±0.2mm; and the installation step includes setting a guide mechanism (42) made of low-friction material on the inner wall of the rectangular through hole (211).

9. A displacement measurement method based on a linear displacement sensor as described in any one of claims 1 to 6, characterized in that, Includes the following steps: a) Feed a microwave signal with a frequency equal to the notch frequency into the input port (12) of the sensor; b) When the upper embedded medium plate (31) is displaced, the reflection phase of the input port (12) is measured in real time; c) Calculate the displacement distance based on the change in the reflection phase and a preset linear sensitivity coefficient.

10. The displacement measurement method according to claim 9, characterized in that, Before calculating the displacement, the linear sensitivity coefficient is determined by moving to a known standard position for calibration; when the cumulative change in the reflected phase exceeds 360 degrees, a phase unwinding algorithm is used for processing; and common-mode noise interference is eliminated by simultaneously measuring the transmission phase of the output port (13) and calculating the difference with the reflected phase.

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