Coplanar dumbbell-shaped sspps liquid level sensor and wireless liquid level sensing system

Abstract

The application discloses a coplanar dumbbell type SSPPs liquid level sensor and a wireless liquid level sensing system, relates to the field of non-contact liquid level detection, and adopts the coplanar dumbbell type SSPPs liquid level sensor to realize non-contact and wireless liquid level detection. The liquid level sensor adopts a flexible structure and can be attached to or integrally formed on the side wall of a to-be-detected container. The wireless liquid level sensor receives an excitation signal and obtains a detection signal. According to phase data corresponding to the detection signal and a phase difference between the phase data and an initial phase, a corresponding liquid level height is calculated. The liquid level sensor can directly measure the liquid level of the to-be-detected container without damaging the structure of the to-be-detected container. The phase change is used as a detection characteristic parameter, so that continuous, monotonic and high-resolution response characteristics are realized in the whole measurement range. Furthermore, the adaptability of the sensor in an industrial application scenario is improved, and the application requirements of compact structure, high reliability and low cost are met.

Description

Technical Field

[0001] This application belongs to the field of non-contact liquid level detection, specifically relating to a coplanar dumbbell-shaped SSPPs liquid level sensor and a wireless liquid level sensing system. Background Technology

[0002] Liquid level refers to the height or position of a liquid in a container, and is a key parameter for the operational stability and process control of a reaction system. In the aerospace field, real-time liquid level monitoring directly affects propellant supply and flight safety; in energy and chemical systems, liquid level monitoring is integral to the entire process of storage, transportation, and chemical reaction; in industrial manufacturing, liquid level monitoring is crucial for system safety, production continuity, and product quality stability. Compared to metal liquid containers, non-metallic liquid containers are widely used for storing toxic, volatile, or highly corrosive liquids due to their advantages such as light weight, corrosion resistance, and ease of molding.

[0003] Traditional contact-based liquid level detection methods (such as float-based, capacitive, pressure-based, and fiber optic methods) are often limited by the risk of contamination and are difficult to adapt to the detection needs of toxic, corrosive, or volatile liquids. Non-contact methods (such as laser, ultrasonic, and radar methods) often employ invasive installation methods like drilling, which can damage the structural integrity of the liquid container, leading to decreased sealing performance and creating potential risks of leakage or contamination. This is especially true in scenarios storing corrosive, volatile, or flammable and explosive liquids, where even minor structural modifications can pose safety risks. Furthermore, existing liquid level sensors are mostly rigid structures, limiting their application in flexible detection scenarios, making integrated deployment of the container and sensor difficult. Additionally, traditional detection systems commonly use wired connections, which are inconvenient for deploying sensors in complex environments and complicate measurements. Based on these challenges, there is an urgent need to develop a novel non-contact wireless sensing technology that can penetrate the walls of non-metallic liquid containers while possessing both flexibility and high sensitivity to meet the diverse and high-performance requirements of next-generation intelligent systems in structural health monitoring and liquid state identification. Summary of the Invention

[0004] To address the limitations of existing liquid level detection technologies, such as difficulty in penetrating containers for direct measurement, reliance on drilling for installation which damages the container structure, and the fact that most are rigid structures limiting the detection scenarios, this application proposes a coplanar dumbbell-shaped SSPPs liquid level sensor and a wireless liquid level sensing system.

[0005] This application is achieved through the following technical solution:

[0006] A coplanar dumbbell-shaped SSPPs level sensor includes: a sensor body and end-fire antennas integrated at both ends of the sensor body;

[0007] The sensor body adopts a flexible coplanar structure, including a first coplanar waveguide feeding section, a first gradient transition section, a sensing and detection section composed of periodic coplanar dumbbell-shaped SSPP units, a second gradient transition section, and a second coplanar waveguide feeding section. The first and second coplanar waveguide feeding sections are used to connect the sensor body to a coaxial line. The first gradient transition section is used to transition between the first coplanar waveguide feeding section and the sensing and detection section. The second gradient transition section is used to transition between the sensing and detection section and the second coplanar waveguide feeding section. The sensing and detection section is used to support the detection of liquid level signals.

[0008] The end-fire antennas at both ends of the sensor body serve as receiving antennas and transmitting antennas, respectively, and the receiving antennas and transmitting antennas are orthogonally designed.

[0009] In some embodiments, the sensing and detection section employs periodically arranged coplanar dumbbell-shaped SSPP units. The coplanar dumbbell-shaped SSPP unit includes a first dielectric substrate and a first copper layer located on the surface of the first dielectric substrate. The first copper layer includes a signal line portion and a ground metal portion. The signal line portion is located in the middle of the surface of the first dielectric substrate, and the ground metal portions are located on both sides of the surface of the first dielectric substrate, with gaps between the signal line portion and the ground metal portions on both sides. The two side edges of the signal line portion are comb-shaped teeth, and the comb-shaped teeth are dumbbell-shaped.

[0010] In some embodiments, the first coplanar waveguide feed portion and the second coplanar waveguide feed portion have the same structure, both including the first dielectric substrate and a second copper layer located on the surface of the first dielectric substrate, and the second copper layer includes a rectangular signal line portion in the middle and ground metal portions on both sides.

[0011] The second copper layer is coplanar with the first copper layer.

[0012] In some embodiments, the first gradient transition portion and the second gradient transition portion have the same structure, both including the first dielectric substrate and a third copper metal layer located on the surface of the first dielectric substrate. The third copper metal layer is coplanar with the first copper metal layer and the second copper metal layer. The third copper metal layer includes a signal line portion in the middle and ground metal portions on both sides. The signal line portion in the third copper metal layer has comb-like teeth on both sides, and the width of the middle metal line of the signal line portion closer to the sensing and detection portion in the third copper metal layer is smaller than the width of the middle metal line of the signal line portion farther away from the sensing and detection portion.

[0013] In some embodiments, the dielectric substrate and the copper layer of the end-fire antenna are made of the same material and have the same thickness as the sensor body.

[0014] In some embodiments, one of the end-fire antennas at both ends of the sensor body is connected to the sensor body through a bent transition structure to achieve an orthogonal design with the other end-fire antenna.

[0015] The radius of the bending transition structure is three times the width of the signal line.

[0016] In some embodiments, the end-fire antenna includes a second dielectric substrate and a coplanar waveguide feed line, a ground metal, and an SSPP transmission line located on the surface of the second dielectric substrate;

[0017] The coplanar waveguide feed line and SSPP transmission line are located in the middle of the surface of the second dielectric substrate. The ground metal is located on both sides of the coplanar waveguide feed line and there is a gap between the ground metal on both sides and the coplanar waveguide feed line. Multiple periodic grooves are etched on one side of the ground metal of the coplanar waveguide feed line to form an asymmetric feeding structure.

[0018] In some embodiments, the grounding metals on both sides of the coplanar waveguide feed line are provided with rounded chamfer transitions, and the radii of the rounded chamfers on the two sides of the grounding metals are different.

[0019] In some embodiments, a trapezoidal metal radiating structure is loaded at the end of the SSPP transmission line.

[0020] On the other hand, this application proposes a wireless liquid level sensing system, comprising:

[0021] A signal generating device is used to generate an excitation signal and radiate it through a second transmitting antenna into the free space where the liquid container under test is located, while simultaneously inputting the excitation signal into a signal processing module;

[0022] The coplanar dumbbell-shaped SSPPs liquid level sensor in any of the above embodiments is attached to or integrally formed on the side wall of the liquid container to be measured. The received excitation signal is input into the sensor body through its end-fire antenna to obtain a detection signal, and the detection signal is radiated into free space through its end-fire antenna.

[0023] And a signal processing module, which receives the detection signal through the second receiving antenna and processes it to obtain the phase data corresponding to the detection signal, and calculates the corresponding liquid level based on the phase shift of the phase data corresponding to the detection signal relative to the initial phase.

[0024] This application proposes a coplanar dumbbell-shaped SSPPs liquid level sensor and a wireless liquid level sensing system. The sensor employs a low-cost passive sensing structure, compatible with standard PCB manufacturing processes, facilitating mass production and system integration. The introduced periodic coplanar dumbbell-shaped SSPP unit structure generates a significant slow-wave effect, enhancing electromagnetic confinement and improving sensitivity. This characteristic not only contributes to system miniaturization and cost reduction but also enhances the sensor's adaptability in industrial applications, meeting the requirements of compact structure, high reliability, and low cost. The liquid level sensor is a flexible structure that can be attached to or integrally molded onto the sidewall of the container under test, directly penetrating the container for measurement without damaging its structure. This enables non-contact and wireless liquid level detection, making it particularly suitable for complex scenarios where direct wiring is impossible or where the liquid environment is harsh, as well as flexible detection scenarios. It uses phase change as the detection characteristic parameter, avoiding the instability and observation ambiguity problems associated with using cutoff frequency as the criterion, thus achieving continuous, monotonic, and high-resolution response characteristics throughout the measurement range. Attached Figure Description

[0025] The accompanying drawings, which are included to provide a further understanding of the embodiments of this application and form part of this application, do not constitute a limitation on the embodiments of this application. In the drawings:

[0026] Figure 1 This is a schematic diagram of the liquid level sensor proposed in the embodiments of this application;

[0027] Figure 2 This is a schematic diagram of the sensor body according to an embodiment of this application;

[0028] Figure 3 This is a schematic diagram of a single coplanar dumbbell-shaped SSPP unit according to an embodiment of this application;

[0029] Figure 4 This is a schematic diagram of an end-fire antenna according to an embodiment of this application;

[0030] Figure 5 This is a block diagram illustrating the principle of the wireless liquid level sensing system proposed in this application.

[0031] Figure 6 The figure shows the S-parameter simulation results of the coplanar dumbbell-shaped SSPPs level sensor proposed in the embodiments of this application and the traditional SSPPs sensor, with the same size.

[0032] Figure 7 S-type end-fire antennas with symmetrical and asymmetrical feed structures 11 Amplitude response curve comparison chart;

[0033] Figure 8 The simulation results for the voltage standing wave ratio and forward / backward ratio of the end-fire antenna are shown in the figure.

[0034] Figure 9 The diagram shows the gain and radiation efficiency distribution of the end-fire antenna.

[0035] Figure 10 This is the polarization pattern of the end-fire antenna;

[0036] Figure 11 The cutoff frequency variation curves and transmission phase variation curves of the liquid level sensor proposed in the embodiments of this application are shown for different liquid levels.

[0037] Figure 12 This illustrates the relationship between the liquid level measurement results and the fitted curve of the wireless liquid level sensing system according to an embodiment of this application.

[0038] Figure 13 The results of liquid level measurement error of the wireless liquid level sensing system in different experimental groups according to the embodiments of this application;

[0039] Figure reference numerals and corresponding component names:

[0040] 1-End-fire antenna, 11-Second dielectric substrate, 12-Coplanar waveguide feed line, 13-Grounding metal, 14-SSPP transmission line, 15-Wire slot, 16-Trapezoidal metal radiating structure, 2-Sensor body, 21-First dielectric substrate, 22-First coplanar waveguide feed section, 23-First gradient transition section, 24-Sensing and detection section, 241-Signal line section, 2411-Comb teeth, 242-Grounding metal section, 25-Second gradient transition section, 26-Second coplanar waveguide feed section, 3-Bent transition structure. Detailed Implementation

[0041] In the following, the terms “comprising” or “may include” as used in the various embodiments of this application indicate the presence of a function, operation, or element of the invention and do not limit the addition of one or more functions, operations, or elements. Furthermore, as used in the various embodiments of this application, the terms “comprising,” “having,” and their cognates are intended only to indicate a specific feature, number, step, operation, element, component, or combination of the foregoing and should not be construed as primarily excluding the presence of one or more other features, numbers, steps, operations, elements, components, or combinations of the foregoing, or adding one or more combinations of the foregoing.

[0042] In various embodiments of this application, the expression "or" or "at least one of A and / or B" includes any combination or all combinations of the words listed simultaneously. For example, the expression "A or B" or "at least one of A and / or B" may include A, may include B, or may include both A and B.

[0043] The terms used in the various embodiments of this application (such as "first," "second," etc.) may modify various constituent elements in the various embodiments, but do not limit the corresponding constituent elements. For example, the above terms do not limit the order and / or importance of the elements. The above terms are only used for the purpose of distinguishing one element from other elements. For example, a first user device and a second user device refer to different user devices, although both are user devices. For example, without departing from the scope of the various embodiments of this application, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element.

[0044] It should be noted that if a description is made of "connecting" one component to another, then the first component can be directly connected to the second component, and a third component can be "connected" between the first and second components. Conversely, when a component is "directly connected" to another component, it can be understood that there is no third component between the first and second components.

[0045] The terminology used in the various embodiments of this application is for the purpose of describing particular embodiments only and is not intended to limit the various embodiments of this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which the various embodiments of this application pertain. The terms (such as those defined in a generally used dictionary) are to be interpreted as having the same meaning as in the context of the relevant technical field and are not to be interpreted as having an idealized or overly formal meaning, unless clearly defined in the various embodiments of this application.

[0046] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the embodiments and accompanying drawings. The illustrative embodiments and descriptions of this application are only for explaining this application and are not intended to limit this application.

[0047] This application proposes a coplanar dumbbell-shaped SSPPs level sensor, which adopts a periodic coplanar dumbbell-shaped SSPP unit structure. The original quasi-TEM mode of the coplanar waveguide is transformed into a TM mode suitable for the SSPPs structure, making it applicable to flexible detection scenarios. At the same time, the introduction of the coplanar waveguide structure can omit the arc-shaped mode conversion structure of traditional SSPPs, reducing the difficulty of transition structure optimization.

[0048] Specifically, such as Figure 1As shown, the liquid level sensor proposed in this embodiment includes a sensor body 2 and end-fire antennas 1 integrated at both ends of the sensor body 2. The end-fire antennas 1 connected to both ends of the sensor body 2 serve as receiving antennas and transmitting antennas, respectively. The end-fire antennas 1 at both ends of the sensor body 2 are designed orthogonally, that is, the end-fire antenna 1 at one end of the sensor body 2 is orthogonally connected to the sensor body 2 through a bending transition structure 3, and the end-fire antenna 1 at the other end is connected to the sensor body 2, so that the signal transmission directions of the end-fire antenna 1 at one end of the sensor body 2 and the end-fire antenna 1 at the other end are perpendicular. The radius of the bending transition structure 3 is set to three times the signal line width (i.e., the signal line width in the middle of the coplanar waveguide feed section) to ensure impedance continuity. This design effectively reduces polarization interference between antennas.

[0049] like Figure 2 As shown, the sensor body 2 adopts a flexible coplanar structure, including a first coplanar waveguide feeding section 22, a first gradient transition section 23, a sensing and detection section 24 composed of periodic coplanar dumbbell-shaped SSPP (Artificial Surface Plasmon Polariton) units, a second gradient transition section 25, and a second coplanar waveguide feeding section 26. The first coplanar waveguide feeding section 22 and the second coplanar waveguide feeding section 26 are used to weld SMA connectors to enable the sensor body 2 to be connected to a 50Ω coaxial cable. The first gradient transition section 23 and the second gradient transition section 25 respectively transition from the first coplanar waveguide feeding section 22 and the second coplanar waveguide feeding section 26 to the sensing and detection section 24, which supports the detection of liquid level signals. Preferably, the width of the first dielectric substrate 21 is... The lengths of the first coplanar waveguide feed section 22 and the second coplanar waveguide feed section 26 The lengths of the first gradient transition portion 23 and the second gradient transition portion 25 The length of the sensing and detection section 24 .

[0050] The sensing and detection section 24 of this embodiment employs periodically arranged coplanar dumbbell-shaped SSPP units. Multiple coplanar dumbbell-shaped SSPP units are periodically arranged along the signal transmission direction to form a periodic unit structure. This periodic unit structure transforms the original TEM mode of the coplanar waveguide into a TM mode suitable for SSPP structures, making it applicable to flexible detection scenarios. Simultaneously, the introduction of the coplanar waveguide structure eliminates the need for the arc-shaped mode conversion structure of traditional SSPPs, reducing the difficulty of transition structure optimization. Specifically, in the sensing and detection section 24 of this embodiment, a single coplanar dumbbell-shaped SSPP unit includes a first dielectric substrate 21 and a copper layer on its surface. The copper layer includes a signal line portion 241 and a ground metal portion 242. The signal line portion 241 is located in the middle of the surface of the first dielectric substrate 21, and the ground metal portions 242 are located on both sides of the surface of the first dielectric substrate 21. Gaps exist between the signal line portion 241 and the ground metal portions 242 on both sides. The signal line portion 241 has dumbbell-shaped comb-like teeth 2411 on both sides. For example... Figure 3 As shown, the width of a single dumbbell-shaped comb tooth 2411 near the gap is... The tooth width away from the gap is The spacing between adjacent comb teeth 2411 along the signal transmission direction is The width of the middle metal wire in the signal line portion 241 is The length of a single coplanar dumbbell-shaped SSPP element is The thickness of the first dielectric substrate 21 is The thickness of the copper layer is Preferably, the length of a single coplanar dumbbell-shaped SSPP unit is... The thickness of the copper layer The thickness of the first dielectric substrate gap The width of the comb-like teeth 2411 Tooth width Tooth spacing The width of the middle metal wire .

[0051] The first coplanar waveguide feed section 22 and the second coplanar waveguide feed section 26 include a first dielectric substrate 21 and a copper layer on its surface. The copper layer is coplanar with the copper layer of the sensing and detection section. The signal lines therein are rectangular, and there are gaps between them and the ground metal portions on both sides. The width is consistent.

[0052] The first gradient transition portion 23 and the second gradient transition portion 25 have similar structures to the sensing and detection portion 24. The only difference is that the width of the middle metal line of the signal line portion on the side of the first gradient transition portion 23 and the second gradient transition portion 25 closer to the sensing and detection portion 24 is smaller than the width of the middle metal line of the signal line portion on the side farther away from the sensing and detection portion 24.

[0053] Furthermore, the end-fire antenna 1 in this embodiment is an integrated transceiver end-fire antenna, used to receive excitation signals and transmit sensing signals. Considering that the sensor body 2 adopts a flexible coplanar structure, in order to ensure good integration between the antenna and the sensor body, the material and thickness of the antenna substrate and the copper layer are consistent with those of the sensor body 2. The feeding method still adopts a coplanar waveguide structure. Specifically, as shown... Figure 4 As shown, the end-fire antenna 1 of this embodiment includes a second dielectric substrate 11 and a coplanar waveguide feed line 12, a ground metal 13, and an SSPP transmission line 14 formed on the second dielectric substrate 11. The coplanar waveguide feed line 12 and the SSPP transmission line 14 are located in the middle of the second dielectric substrate 11. The ground metal 13 is located on both sides of the coplanar waveguide feed line 12, and there are gaps between the ground metal 13 on both sides and the coplanar waveguide feed line 12. Several periodically arranged slots 15 are etched on one side of the ground metal 13 of the coplanar waveguide feed line 12 to form an asymmetric feeding structure, thereby enhancing mode coupling and impedance matching capabilities. Simultaneously, the ground metal 13 on both sides is designed with rounded chamfer transitions, and the radii of the rounded chamfers on both sides are different, to improve the impedance matching of the transition from the asymmetric feeding structure to the SSPP transmission line 14. Furthermore, to improve radiation efficiency, a trapezoidal metal radiation structure 16 is loaded at the end of the SSPP transmission line 14, thereby achieving efficient spatial radiation of energy. Preferably, the overall length of the end-fire antenna is... In this end-fire antenna, the width of the second dielectric substrate 11 is the same as the width of the first dielectric substrate 21, which is 40mm, and the thickness of the second dielectric substrate 11 is the same as the thickness of the first dielectric substrate 21, which is 0.07mm; the trapezoidal width at the end of the SSPP transmission line 14... The lengths of the coplanar waveguide feeder 12 and the grounding metal 13 are... ; Length of a single wire trough 15 in the grounding metal 13 Width of groove 15 The spacing between the 15 wire troughs The circular chamfer radius of the grounding metal 13 on one side, which is engraved with periodic grooves 15. The circular chamfer radius of the grounding metal 13 on the side without periodic wire groove 15 The gap between the coplanar waveguide feed line 12 and the grounding metal 13 on both sides is the same as the aforementioned gap. The same, 0.23mm; the width of coplanar waveguide feed 12 is 4.5mm.

[0054] The liquid level sensor proposed in this application is a surface electromagnetic wave excited at a metal-dielectric interface, formed by the interaction between the incident electromagnetic wave and free electrons on the metal surface. Its detection principle is as follows: this type of electromagnetic wave propagates along the metal-dielectric interface, and its propagation characteristics are extremely sensitive to changes in the interface's electromagnetic environment. During measurement, when the presence of the liquid medium alters the electromagnetic environment of the metal-dielectric interface, the propagation characteristics of the electromagnetic wave along the transmission line will also change accordingly. To characterize the phase characteristics of the electromagnetic wave during propagation, a phase constant is typically used. The mathematical expression for this description is as follows:

[0055] ;

[0056] in, At the speed of light, For operating frequency, is the equivalent dielectric constant of the medium.

[0057] Assuming the propagation path of the microwave signal is parallel to the height direction of the liquid, then the propagation path... The field distribution in the effective length of the liquid level sensor's detection area consists of two parts: one part is the liquid being measured (with a height of...). Its relative permittivity The other part is air (at an altitude of...). Its relative permittivity .because Then the phase characteristics It can be represented as:

[0058] ;

[0059] in,

[0060] ;

[0061] in, Let be the phase shift constants of the liquid and air, respectively. Assume the liquid level rises from... Change to The corresponding phase shift characteristics are as follows: The resulting phase shift Then it is:

[0062] ;

[0063] Therefore, we get:

[0064] ;

[0065] Introducing a proportionality coefficient Then phase shift change and liquid level change The relationship can be further expressed as:

[0066] ;

[0067] ;

[0068] Based on the above derivation, it can be seen that the phase shift change and the liquid level change have a linear relationship, and the proportionality coefficient is... The liquid level is mainly determined by the operating frequency of the liquid level sensor and the relative permittivity of the liquid being measured. Based on this, the liquid level sensor proposed in this application can achieve liquid level measurement by measuring the phase change of the signal.

[0069] The liquid level sensor proposed in this application is a flexible mechanism that can be attached to or integrally formed onto the sidewall of the container to be measured. It directly penetrates the container for measurement without damaging the container structure, thus achieving non-contact and wireless liquid level detection. It is particularly suitable for complex scenarios where direct wiring is not possible or where the liquid environment is harsh, as well as flexible detection scenarios. It uses phase change as the detection characteristic parameter, avoiding the instability and observation ambiguity problems that exist when using the cutoff frequency as the criterion, thereby achieving continuous, monotonic, and high-resolution response characteristics throughout the measurement range. In terms of structural design, the sensor adopts a low-cost passive sensing structure and is compatible with standard PCB manufacturing processes, which is conducive to mass production and system integration. At the same time, the introduced periodic coplanar dumbbell-shaped SSPP unit structure can generate a significant slow wave effect, thereby enhancing the electromagnetic field confinement capability and improving phase sensitivity. This characteristic not only helps to achieve system miniaturization and low cost, but also further improves the adaptability of the sensor in industrial application scenarios, meeting the application requirements of compact structure, high reliability, and low cost.

[0070] Furthermore, based on the aforementioned coplanar dumbbell-shaped SSPPs liquid level sensor, this application embodiment constructs a wireless liquid level sensing system, specifically as follows: Figure 5 As shown, the wireless liquid level sensing system includes:

[0071] The signal generating device is used to generate an excitation signal and radiate it into the free space where the liquid level container to be measured is located via the second transmitting antenna (i.e. the transmitting antenna on the signal generating device side). At the same time, the excitation signal is input to the signal processing module as a reference.

[0072] The coplanar dumbbell-shaped SSPPs liquid level sensor is attached to or integrally formed on the side wall of the container containing the liquid to be measured. The received excitation signal is input into the sensor body through its end-emitting antenna to obtain the detection signal, and the detection signal is radiated into free space through its end-emitting antenna.

[0073] Additionally, a signal processing module receives and processes the detection signal through a second receiving antenna (i.e., the receiving antenna on the signal processing module side) to obtain the phase data corresponding to the detection signal, and calculates the corresponding liquid level based on the difference between the phase data corresponding to the detection signal and the initial phase.

[0074] The working process of this wireless liquid level sensing system includes:

[0075] First, a fixed-frequency excitation signal (with phase 1) is generated by a signal generator. The excitation signal is radiated into the free space where the liquid container under test is located through the second transmitting antenna, and at the same time the excitation signal is input to the signal processing module as a reference;

[0076] Then, the liquid level sensor, which is attached to the side wall of the container containing the liquid to be measured, transmits the received excitation signal to the sensor body through the end-fire antenna (receiving antenna) to obtain the detection signal (phase is The detection signal is radiated into free space through the end-fire antenna (transmitting antenna);

[0077] Subsequently, the second receiving antenna inputs the detection signal into the signal processing module to obtain the phase data of the detection signal;

[0078] By repeating the above process, detection signals for different liquid levels can be obtained. The detection signals for different liquid levels have a certain phase shift from the initial detection signal. This phase shift is linearly related to the liquid level to be measured. Therefore, based on the detection principle of the sensor, the liquid level difference can be calculated from the phase deviation. Given the initial liquid level, the current liquid level can be calculated, thus enabling wireless detection of liquid level changes.

[0079] It is understandable that, in order to facilitate data processing, the embodiments of this application can use the above-mentioned wireless liquid level sensing system to detect the liquid level container under test in a liquid-free state before actual detection, obtain the phase corresponding to zero liquid level and use it as the initial phase, so that only the difference between the phase obtained from each detection and the initial liquid level is needed to directly obtain the corresponding liquid level data, without the need to obtain the initial liquid level.

[0080] To verify the performance of the liquid level sensor proposed in the embodiments of this application:

[0081] (1) The transmission performance of a sensor composed of typical SSPP units of the same period length (i.e., SSPPs) and a coplanar dumbbell-shaped SSPPs (i.e., CD-SSPPs) level sensor proposed in the embodiments of this application were simulated and analyzed. The S-parameter simulation curves are shown in the figure below. Figure 6 As shown. By Figure 6As can be seen, the cutoff frequency of the coplanar dumbbell-shaped SSPPs level sensor proposed in this application embodiment is about 11.27 GHz, while the cutoff frequency of a typical SSPPs sensor is about 18.88 GHz. This result shows that the coplanar dumbbell-shaped SSPPs level sensor proposed in this application embodiment achieves a relative size reduction of about 40.7%.

[0082] (2) To further analyze the impact of asymmetric feeding structures on the electromagnetic characteristics of end-fire antennas, two structural models, symmetric and asymmetric, were constructed and full-wave electromagnetic simulations were conducted, yielding the following results: Figure 7 The two types of bottom-firing antennas shown have S-shaped structures. 11 Amplitude response curve. (From...) Figure 7 As can be seen, the end-fire antenna with an asymmetric feed structure achieves a wider operating bandwidth (5.28 GHz to 7.13 GHz) at the -10 dB threshold, and a significantly reduced overall VSWR, exhibiting superior impedance matching characteristics and radiation consistency. The main reason for this performance improvement is that the periodic grooves etched in the asymmetric grounding metal can form multiple series inductor elements in electromagnetic equivalent, altering the resonance conditions of the original transmission path, thereby optimizing the input impedance characteristics and enhancing the coupling and radiation efficiency of electromagnetic energy.

[0083] (3) To verify the performance of the end-fire antenna, simulation tests were performed on the end-fire antenna proposed in the embodiments of this application, and the results were obtained. Figure 8 The end-fire antenna shown has a voltage standing wave ratio (VSWR) of less than 1.27 at 6 GHz, and the VSWR remains below 1.7 throughout the entire passband, reflecting excellent impedance matching performance. At the same time, the front-to-back ratio (FBR) exceeds 5.99 at 6 GHz, and can reach up to 7.9 throughout the entire frequency band. This result indicates that the end-fire antenna has good directivity characteristics.

[0084] Figure 9 The gain and efficiency distribution of the end-fire antenna are shown. The end-fire gain ranges from 2.47 dBi to 4.79 dBi, reaching 4.39 dBi at 6 GHz. The maximum radiation efficiency is 95% across the entire operating band, reaching 87% at 6 GHz, demonstrating high energy conversion efficiency.

[0085] Figure 10The normalized radiation patterns of the end-fire antenna in the E-plane (xoy plane) and H-plane (yoz plane) are further presented to verify its excellent end-fire radiation characteristics. The results show that the cross-polarization and sidelobe levels remain below -18.38 dB and -15.5 dB, respectively, in the E-plane. This indicates that the antenna possesses good polarization purity and radiation direction control capability. Furthermore, at 6 GHz, the antenna's 3 dB beamwidth is [missing information - likely a percentage] of the E-plane [missing information - likely a percentage]. H-plane Based on the above analysis, the proposed end-fire antenna not only has strong directivity and high radiation efficiency, but also exhibits broadband characteristics, which can provide stable electromagnetic radiation support for subsequent wireless liquid level sensing.

[0086] (4) To verify the correctness of the simulation results and the performance of the liquid level sensor, a corresponding liquid level sensor was further fabricated and a corresponding wireless liquid level sensing system experimental platform was built. The liquid level sensor was attached to the side wall of the liquid level container. The end-fire antennas at both ends of the liquid level sensor needed to extend beyond the edge of the liquid container. During the experiment, a pair of identical horn antennas (i.e., the second transmitting antenna and the second receiving antenna) were used to excite and receive signals from the end-fire antennas at both ends of the sensor. The selected horn antennas could cover the operating frequency band of the sensor end-fire antenna and the bandwidth near the cutoff frequency of the transmission line, and maintain a stable gain of more than 12 dBi in the 8–12 GHz range. The two horn antennas were placed orthogonally to each other, and their horn mouth planes were perpendicular to the sensor end-fire antennas. The distance between the horn antennas and the sensor end-fire antennas was fixed at 0.5 cm. The signal was transmitted through near-field coupling. The liquid container used in the experiment was made of polytetrafluoroethylene, and small holes were opened on the side wall for injecting or withdrawing liquid through a syringe to achieve liquid level regulation. The signal path passed through the excitation horn antenna, the sensor receiving antenna, the sensor body and the sensor transmitting antenna in sequence, and was finally read by the receiving horn antenna. The S of the system 21 Amplitude and phase are measured and recorded by a vector network analyzer.

[0087] Before conducting the liquid level detection experiment, the vector network analyzer was fully preheated to ensure stable operation. Standard calibrations for open circuit, short circuit, and load conditions were then performed sequentially to eliminate systematic errors and improve measurement accuracy and reusability. After calibration, edible oil was slowly injected into a non-metallic container using a syringe, gradually adjusting the liquid level. The sensor transmission parameter S was collected and recorded after each level adjustment. 21 From the amplitude and phase data, we can obtain Figure 11 The curves showing the cutoff frequency variation and transmission phase variation of the liquid level sensor proposed in this application at different liquid levels are illustrated in the figure. As can be seen from the figure, with increasing liquid level... As the liquid level increases, the cutoff frequency of the sensor decreases, but the change is small and difficult to observe; while with the increase in liquid level... As the liquid level increases, the transmission phase of the sensor gradually decreases, with the change pattern approximating an arithmetic progression. Therefore, the phase characteristics of the liquid level sensor proposed in this embodiment can more intuitively reflect the liquid level change pattern and avoid identification errors caused by nonlinear changes in the cutoff frequency. Considering the transition structure between the sensor body and the antenna, to ensure the consistency of the liquid level reference, the zero liquid level reference point is set above this transition region. Test results show that the sensor's no-load cutoff frequency is approximately 8.12 GHz, slightly different from the simulation results. This difference mainly stems from dimensional tolerances during manufacturing and the difference between the actual container medium parameters and the simulation settings. To further analyze the impact of liquid level changes on transmission characteristics, the phase change in the 6 GHz band (within the passband) is selected as the core characterization parameter, and its variation is recorded under different liquid level conditions. Based on the experimental data, curve fitting is used to establish a functional relationship between the liquid level height and the sensor output phase offset, and regression analysis is performed to evaluate its linear characteristics. Figure 12 and Figure 13 As shown, the fitted curve is highly consistent with the measured data, exhibiting a stable linear relationship throughout the entire measurement range, indicating that the sensor can achieve high-precision and continuous liquid level sensing. Based on the fitting results, the sensor's sensitivity is calculated to be... This demonstrates its remarkable responsiveness to minute changes in liquid level. The error between the measured and theoretical phase shift at room temperature was controlled within a certain range. The corresponding relative error is 0.87 mm. ).

[0088] In summary, the CD-SSPPs level sensor based on phase shift characteristics exhibits excellent stability and repeatability in level detection, achieving not only high linearity and resolution but also good environmental adaptability and engineering feasibility.

[0089] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this application. It should be understood that the above description is only a specific embodiment of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A coplanar dumbbell-shaped SSPPs level sensor, characterized in that, include: The sensor body and the end-fire antennas integrated at both ends of the sensor body; The sensor body adopts a flexible coplanar structure, including a first coplanar waveguide feeding section, a first gradient transition section, a sensing and detection section composed of periodic coplanar dumbbell-shaped SSPP units, a second gradient transition section, and a second coplanar waveguide feeding section. The first and second coplanar waveguide feeding sections are used to connect the sensor body to a coaxial line. The first gradient transition section is used to transition between the first coplanar waveguide feeding section and the sensing and detection section. The second gradient transition section is used to transition between the sensing and detection section and the second coplanar waveguide feeding section. The sensing and detection section is used to support the detection of liquid level signals. The end-fire antennas at both ends of the sensor body serve as receiving and transmitting antennas, respectively, and the receiving and transmitting antennas are orthogonally designed. The coplanar dumbbell-shaped SSPP unit includes a first dielectric substrate and a first copper layer on the surface of the first dielectric substrate. The first copper layer includes a signal line portion and a ground metal portion. The signal line portion is located in the middle of the surface of the first dielectric substrate, and the ground metal portions are located on both sides of the surface of the first dielectric substrate, with gaps between the signal line portion and the ground metal portions on both sides. The two side edges of the signal line portion are comb-shaped teeth, and the comb-shaped teeth are dumbbell-shaped. One of the end-fire antennas at both ends of the sensor body is connected to the sensor body through a bent transition structure to achieve an orthogonal design with the other end-fire antenna. The radius of the bending transition structure is three times the width of the signal line.

2. The coplanar dumbbell-shaped SSPPs level sensor according to claim 1, characterized in that, The first coplanar waveguide feeding section and the second coplanar waveguide feeding section have the same structure, both including the first dielectric substrate and a second copper metal layer located on the surface of the first dielectric substrate, and the second copper metal layer includes a rectangular signal line portion in the middle and ground metal portions on both sides. The second copper layer is coplanar with the first copper layer.

3. The coplanar dumbbell-shaped SSPPs level sensor according to claim 2, characterized in that, The first gradient transition portion and the second gradient transition portion have the same structure, both including the first dielectric substrate and a third copper metal layer on its surface. The third copper metal layer is coplanar with the first copper metal layer and the second copper metal layer. The third copper metal layer includes a signal line portion in the middle and ground metal portions on both sides. The signal line portion in the third copper metal layer has comb-like teeth on both sides, and the width of the middle metal line of the signal line portion closer to the sensing and detection portion in the third copper metal layer is smaller than the width of the middle metal line of the signal line portion farther away from the sensing and detection portion.

4. A coplanar dumbbell-shaped SSPPs level sensor according to any one of claims 1-3, characterized in that, The dielectric substrate and the copper layer of the end-fire antenna are made of the same material and have the same thickness as the sensor body.

5. A coplanar dumbbell-shaped SSPPs level sensor according to claim 4, characterized in that, The end-fire antenna includes a second dielectric substrate and a coplanar waveguide feed line, a ground metal, and an SSPP transmission line located on the surface of the second dielectric substrate. The coplanar waveguide feed line and SSPP transmission line are located in the middle of the surface of the second dielectric substrate. The ground metal is located on both sides of the coplanar waveguide feed line and there is a gap between the ground metal on both sides and the coplanar waveguide feed line. Multiple periodic grooves are etched on one side of the ground metal of the coplanar waveguide feed line to form an asymmetric feeding structure.

6. A coplanar dumbbell-shaped SSPPs level sensor according to claim 5, characterized in that, The grounding metals on both sides of the coplanar waveguide feed line are provided with rounded chamfer transitions, and the radii of the rounded chamfers on the two sides of the grounding metals are different.

7. A coplanar dumbbell-shaped SSPPs level sensor according to claim 5, characterized in that, The SSPP transmission line is fitted with a trapezoidal metal radiating structure at its end.

8. A wireless liquid level sensing system, characterized in that, include: A signal generating device is used to generate an excitation signal and radiate it through a second transmitting antenna into the free space where the liquid container under test is located, while simultaneously inputting the excitation signal into a signal processing module; The coplanar dumbbell-shaped SSPPs liquid level sensor according to any one of claims 1-7 is attached to or integrally formed on the side wall of the liquid container to be measured, and inputs the received excitation signal into the sensor body through its end-fire antenna to obtain a detection signal and radiates the detection signal into free space through its end-fire antenna. And a signal processing module, which receives the detection signal through the second receiving antenna and processes it to obtain the phase data corresponding to the detection signal, and calculates the corresponding liquid level based on the phase shift of the phase data corresponding to the detection signal relative to the initial phase.

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