Double-sided adhesive liquid dielectric constant detection microwave sensor

Abstract

The application discloses a double-sided attached liquid dielectric constant detection microwave sensor and belongs to the technical field of microwave sensors. The sensor mainly comprises a thin-wall container 3, a metal defect-free film 1 closely attached to the inner wall of the thin-wall container 3, and a metal microstrip line film 2 attached to the outer wall of the thin-wall container 3; the metal defect-free film 1 and the metal microstrip line film 2 are attached to the inner and outer walls of the same part of the thin-wall container 3, and the lower edges of the two films are flush; the metal defect-free film 1 is composed of a flexible dielectric substrate 5 and a metal reference ground 4 printed on the flexible dielectric substrate 5, the metal reference ground 4 is etched with a nested complementary split ring resonator (NCSRR) 10, and the NCSRR 10 is a dumbbell-shaped CSRR 21 internally nested with a dumbbell-shaped split ring resonator (SRR) 22 which is the same in shape. The microwave sensor is not limited to a rigid flat plate structure, can be used on some substrates with arc shapes, and makes the selection of the substrate more flexible; the new resonance structure NCSRR is proposed, so that the sensitivity is significantly improved, and the quality factor is also improved correspondingly.

Description

Technical Field

[0001] This invention belongs to the field of microwave sensor technology, and specifically relates to a microwave sensor for detecting the dielectric constant of liquids. Technical Background

[0002] Microwave detection technology enables non-destructive and real-time detection. Microwave metamaterial resonant sensors are formed by sputtering small subwavelength metal resonant elements onto a substrate, offering advantages such as miniaturization and low cost. The measurement principle of microwave metamaterial resonant sensors is simple, primarily based on changes in the dielectric properties of the measured object (DAMP). The DAMP, acting as part of the resonator, resonates under electromagnetic excitation in a specific direction. In the resonant state, the resonator generates a very high-intensity electric field in the capacitance gap. Furthermore, during resonance, a large amount of surface current circulates around the metal ring element. The electric field in this capacitive region is highly sensitive to changes in the dielectric properties within the region; changes in the dielectric properties of the DAMP placed there will cause a shift in the resonant frequency. Based on this principle, microwave resonant sensors are commonly used for measuring dielectric constants. The response of liquid materials to high-frequency electromagnetic signals depends on the complex dielectric constant of the liquid material; therefore, most metamaterial sensors are used for detecting the dielectric constant of liquids.

[0003] Currently, most planar resonant microwave sensors use a three-layer structure: a microstrip transmission line, a dielectric layer, and a ground plane. Microwave sensors are constructed by directly printing the metal microstrip structure and ground plane onto a rigid substrate, resulting in a rigid planar structure. Mustafa Suphi Gulsu et al. measured and estimated the complex permittivity of several liquids by injecting them into a capillary glass tube vertically fixed at the center of a rigid microwave resonant cavity (Gulsu MS, Bagci F, Can S, et al. Minkowski-like fractal resonator-based dielectric sensor for estimating the complex permittivity of binary mixtures of ethanol, methanol and water[J]. Sensors and Actuators A: Physical, 2021, 330:112841.). Rigid microwave sensors require the design of dedicated microchannels around the resonator to detect the dielectric constant of the test liquid, which complicates the testing process and increases costs. Meanwhile, because the liquid sample that can be carried in the microchannel is very small, it is not representative in industrial applications; on the other hand, the microchannel aperture is small and cannot pass through liquids with high viscosity, which means that this type of sensor can only measure a portion of the liquid.

[0004] Over the past decade, flexible devices have demonstrated tremendous potential across various fields. With the widespread adoption of wearable devices, the application of traditional rigid sensors has become somewhat limited, which has also presented new directions for the development of microwave sensors. Combining microwave metamaterial resonant sensors with flexible sensor technology will make the application scenarios of metamaterial sensors more flexible.

[0005] Because some chemical liquids, such as colorless liquids like methanol, hexane, and acetone, are toxic and corrosive, potentially causing serious harm to the human body, it is particularly important to use special materials as dielectric substrates for contactless measurement of the dielectric constant of certain special liquids. Based on these technical issues, this invention proposes a microwave sensor for detecting the dielectric constant of large-sample liquids. This sensor is fabricated using flexible manufacturing processes, meeting the requirements for measuring the dielectric constant of liquids in various scenarios. Summary of the Invention

[0006] To address the above-mentioned technical problems, this invention provides a microwave sensor for detecting the dielectric constant of liquids. This sensor is fabricated using a flexible, attachable thin film, and features a simple sensor structure and manufacturing process, fast response speed, high test sensitivity, large measurement range, and simple testing procedure.

[0007] The present invention adopts the following technical solution:

[0008] A double-sided attached liquid dielectric constant detection microwave sensor mainly includes: a thin-walled container 3, a metal defect ground film 1 tightly attached to the inner wall of the thin-walled container 3, and a metal microstrip line film 2 attached to the outer wall of the thin-walled container 3.

[0009] Furthermore, the metal defect ground film 1 and the metal microstrip line film 2 are the same size, the upper edges of the metal defect ground film 1 and the metal microstrip line film 2 are flush with the opening edge of the thin-walled container 3, the metal defect ground film 1 and the metal microstrip line film 2 are attached to the inner and outer walls of the same part of the thin-walled container 3, and the lower edges of the two films are flush.

[0010] The metal defect ground film 1 is composed of a flexible dielectric substrate 5 and a metal reference ground 4 printed on the flexible dielectric substrate 5. Nested complementary open-circuit resonant rings (NCSRR) 10 are etched on the metal reference ground 4. The side of the metal defect ground film 1 without the metal reference ground is attached to the inner wall of the thin-walled container 3 by ultra-thin double-sided adhesive tape 8.

[0011] The nested complementary split-ring resonator (NCSRR) 10 is derived from the complementary split-ring resonator (CSRR) and is used to improve the resonant characteristics of the sensor's microwave circuit. It can be viewed as a dumbbell-shaped CSRR 21 symmetrical about the opening, inside which is nested a dumbbell-shaped split-ring resonator (SRR) 22 of the same shape. The ring width of the inner split-ring resonator 22 is generally taken as a fraction of the ring width of the outer complementary split-ring resonator 21. The opening distance of the inner resonant ring 22 is generally 1.5 to 3 times the opening distance of the outer opening ring 21, and the distance between the lower edge of NCSRR10 and the lower edge of the metal reference ground is more than 0.5 times the outer side length of CSRR21.

[0012] The metal microstrip film 2 consists of a flexible dielectric substrate 7 and U-shaped microstrip lines 6 printed on the flexible dielectric substrate 7. The side of the metal microstrip film 2 without microstrip lines 6 is attached to the outer wall of the thin-walled container 3 by ultra-thin double-sided adhesive tape 9.

[0013] The U-shaped microstrip line 6 is used to excite the NCSRR resonant unit to generate resonance. The two ends of the U-shaped microstrip line 6 are flush with one side edge of the flexible dielectric substrate 7. The two right-angle bends of the U-shaped microstrip line 6 are beveled at 45° to ensure that the ratio of the distance from the 45° beveled edge to the outer corner to the distance from the inner corner to the outer corner is 0.7~0.8.

[0014] Furthermore, during the attachment process, ensure that the transverse microstrip portion of the U-shaped microstrip line 6 is aligned with the opening portion of the NCSRR10; and ensure that the opening ring is located at the center of the transverse portion of the U-shaped microstrip line.

[0015] The sensor is a dual-port microwave resonant sensor. The two ports of the U-shaped microstrip line 6 are soldered to the metal reference ground 4 and the female connector 11 of the radio frequency coaxial line through connector pins.

[0016] More preferably, the thin-walled container 3 can be an open container of any shape with uniform sidewall thickness, and its wall thickness is 0.5mm~3mm. The height and volume of the thin-walled container 3 are not required and can be selected arbitrarily according to the specific application scenario. The material is a non-conductive material with stable dielectric properties, such as glass, polypropylene, silicone, etc.

[0017] More preferably, the thickness of the flexible dielectric substrates 4 and 7 is between 0.01 mm and 0.1 mm. The size of the dielectric substrate can be adjusted according to the size of the thin-walled container 3 and the application scenario. The material is generally a flexible, dielectrically stable non-conductive material such as polyimide (PI).

[0018] More preferably, the thickness of the metal reference ground 4 and the U-shaped microstrip line 6 is between 0.01mm and 0.05mm, and the material is generally a conductive metal such as copper, gold, or tin. The linewidth of the U-shaped microstrip line 6 is determined by the impedance of the microstrip line and the material and wall thickness of the thin-walled container 3. A suitable linewidth is selected to achieve impedance matching. The vertical length of the U-shaped microstrip line 6 only needs to meet the measurement requirements, and is generally more than 1 times its horizontal length. Its horizontal length is more than 1.5 times the outer side length of the NCSRR10.

[0019] Even better, to ensure the sensor's working performance, the thickness of ultra-thin double-sided adhesive tapes 8 and 9 is generally below 0.05mm.

[0020] Compared with existing liquid dielectric constant detection sensors, the present invention has the following advantages:

[0021] The present invention changes the rigid structure of the previous microwave sensor in terms of structure. It adopts a process of pre-preparing the sensor film and then attaching the flexible film to both sides of the container. This makes the microwave sensor no longer limited to the rigid plate structure and can be used on some curved substrates, making the choice of substrate more flexible.

[0022] A novel resonant structure, NCSRR, was proposed. Compared with the SRR and CSRR structures used to measure the dielectric constant of liquids, the sensor using the NCSRR structure has significantly improved sensitivity and quality factor.

[0023] A U-shaped microstrip line is used to excite the resonant ring. The vertical microstrip line port is easy to connect to the radio frequency coaxial line, which allows the thin film to be used on some open containers to measure the dielectric constant of liquids.

[0024] Using thin-walled containers as the medium substrate eliminates the need to design flow channels to carry the liquid, simplifying the design and reducing costs. The dielectric constant can be tested simply by pouring the liquid sample into the container, simplifying the testing process. When using corrosion-resistant materials as the container material, corrosion problems can also be solved.

[0025] Furthermore, when testing special liquids and other special applications, the required sensor can be assembled simply by replacing the microstrip film according to the dielectric properties and wall thickness of the container. This simplifies the sensor fabrication process and greatly reduces testing costs.

[0026] Other advantages, objectives and features of the present invention will be set forth in the following description. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the front structure of a double-sided attached liquid dielectric constant detection microwave sensor provided by the present invention;

[0028] Figure 2 This is a schematic diagram of the back structure of a double-sided attached liquid dielectric constant detection microwave sensor provided by the present invention;

[0029] Figure 3 This is a schematic diagram of the structure of the thin film with metal defects provided by the present invention;

[0030] Figure 4 This is a schematic diagram of the structure of the metal microstrip thin film provided by the present invention;

[0031] Figure 5 This is a schematic diagram of the nested complementary open resonant ring structure of a double-sided attached liquid dielectric constant detection microwave sensor provided by the present invention.

[0032] Figure 6 This is a schematic diagram of using the present invention to detect the dielectric constant of a liquid;

[0033] Figure 7 This is a graph showing the relationship between the dielectric constant of the liquid under test and the resonant frequency of the sensor, obtained through simulation in this invention.

[0034] Figure 8 The figure shows the fitting graph of the functional relationship between the dielectric constant of the liquid under test and the resonant frequency obtained by simulation in this invention.

[0035] Reference numerals: 1-Metal defect ground film, 2-Metal microstrip film, 3-Thin-walled container acting as substrate, 4-Metal reference ground, 5-Flexible dielectric substrate, 6-U-shaped metal microstrip line, 7-Flexible dielectric substrate, 8, 9-Ultra-thin double-sided adhesive, 10-Nested complementary open resonant ring, 11-Coaxial connector female. Detailed Implementation Plan

[0036] To more clearly illustrate the purpose, technical solution, and advantages of this invention, specific examples are provided below to explain the implementation of the invention. Those skilled in the art can easily understand other advantages and effects of this invention from the content disclosed in this specification. It should be understood that this invention can also be implemented or applied through other different specific embodiments and is not intended to limit the invention. Furthermore, the technical features and illustrations involved in the following embodiments are only schematic representations of the basic concept of the invention; the technical features involved can be combined with each other unless there is conflict. In addition, the resonant ring structure used on the metal defect ground thin film described in this invention is not limited to the nested complementary open resonant ring mentioned herein; open resonant rings, complementary open resonant rings, etc., can be used in different scenarios.

[0037] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0038] Figure 1 , Figure 2 This invention provides a schematic diagram of a double-sided attached microwave sensor for detecting the dielectric constant of a liquid. 1 represents a metal defect ground film, 2 represents a metal microstrip line film, 3 represents a thin-walled container made of borosilicate glass, and 11 represents a 50-ohm coaxial connector female. The metal defect ground film 1 and the metal microstrip film 2 are attached to the same location on the inner and outer walls of the borosilicate glass container 3 to allow the microstrip line 6 to feed the defect structure 10. Nested complementary open-circuit resonant rings (NCSRRs) 10 are etched on the metal defect ground film 1 to improve the resonance characteristics of the sensor's microwave circuit. The metal microstrip line film 2 carries a U-shaped microstrip line 6 to excite the NCSRR 10 to resonate. The two ends of the microstrip line 6 are soldered to the female connector 11 of the RF pass axis via connector pins for connection to a vector network analyzer for testing. The borosilicate glass container 3 plays two key roles in this invention. The portion of the borosilicate glass 3 that adheres to the thin film acts as a dielectric substrate; the thickness and dielectric properties of this portion affect the sensor's performance. Simultaneously, the borosilicate glass container 3 also serves to hold the liquid to be measured. This eliminates the need for an additional liquid-carrying channel, saving costs and simplifying the measurement process. The borosilicate glass used has a dielectric constant of 4.7 and a dielectric loss of 0.0038. The borosilicate glass container is cylindrical with a uniform wall thickness of 2 mm, a height of 80 mm, an outer diameter of 28 mm, and a volume of 150 ml, making the sensor suitable for measuring large-volume samples.

[0039] Figure 3 , Figure 4 These are the metal defect ground film 1 and the metal microstrip film 2 used to fabricate the sensor in this invention. The metal reference ground 4 is perfectly matched in size to the flexible dielectric substrate 5, that is, the length of film 1 is 60mm and the width is 40mm. The material used for the metal reference ground 4 is metallic copper, and its thickness is 35mm. The flexible dielectric substrate 5 is made of polyimide with a dielectric constant of 3.5 and a dielectric loss of 0.004. Its thickness is 50 mm. The size of the metal microstrip film 2 is the same as that of the metal defect ground film 1, wherein the flexible dielectric substrate 7 is also polyimide with a thickness of 50 μm. The U-shaped microstrip line 6, with a length of 60 mm and a width of 40 mm, is made of copper. Its characteristic impedance is 50 ohms to meet impedance matching requirements. It has a vertical length of 48.4 mm, a horizontal length of 26 mm, a linewidth of 3.2 mm, a 45° chamfer at the corner, and a hypotenuse length of 5.12 mm. Both the metal defect ground film 1 and the metal microstrip line film 2 are flexible structures that can be bent at any angle. The 3M966 ultra-thin double-sided adhesive has a dielectric constant of 2.92, a dielectric loss of 0.025, and a thickness of 50 mm. The double-sided adhesive is fully bonded to the flexible dielectric substrate, measuring 60mm in length and 40mm in width. When forming the microwave sensor, the adhesive side needs to be firmly attached to the side wall of the glass container. Notably, the size of this film can be flexibly adjusted according to the size of the container.

[0040] Figure 5 This invention provides a nested complementary open-circuit resonant ring 10 (NCSRR) for a double-sided attached microwave sensor for detecting the dielectric constant of a liquid. The resonant ring is etched onto a metal reference ground. The structural dimensions are as follows: a=10, b=2mm, c=0.25mm, d=0.5mm, g=0.5mm; the lower edge of the NCSRR structure is 5mm from the lower edge of the metal reference ground, and the left edge of the NCSRR is 14mm from the left edge of the metal reference ground.

[0041] Figure 6 This diagram illustrates the detection of the dielectric constant of a liquid using an embodiment of the present invention. During detection, the liquid to be tested is directly placed in a beaker, ensuring the liquid level submerges the NCSRR10 structure. The two ports of the sensor are connected to a vector network analyzer to read the resonant frequency. The read resonant frequency is transmitted to a computer and matched with the dielectric constant to establish a model, allowing for the analysis of the dielectric constant of the unknown liquid.

[0042] Figure 7 The graph shows the relationship between relative permittivity and resonant frequency obtained from simulations of an example of this invention. As can be seen from the graph, as the permittivity of the test liquid increases, the sensor's resonant frequency shifts to the left. When the permittivity changes from 2 to 10, the sensor's resonant frequency decreases from 1.755 GHz to 1.355 GHz. The shift is 0.4 GHz, the unit shift is 50 MHz, and the sensitivity is 3%.

[0043] Figure 8 This is a simulation plot showing the functional relationship between the liquid dielectric constant and the sensor resonant frequency obtained from an example of the present invention. By fitting the obtained dielectric constant and resonant frequency data, a numerical relationship between the dielectric constant and the sensor resonant frequency (GHz) is obtained:

[0044] ,in Let be the dielectric constant of the liquid. It is the resonant frequency.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention. Those skilled in the art can easily understand that the above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. The present invention is not limited to the above examples. Modifications or equivalent substitutions made within the principles of the technical solutions of the present invention, as long as they meet the requirements of the method of the present invention, should be covered within the protection scope of the present invention.

Claims

1. A double-sided attached microwave sensor for detecting the dielectric constant of a liquid, characterized in that, include: Thin-walled container (3), a metal defect film (1) tightly attached to the inner wall of the thin-walled container (3), and a metal microstrip film (2) attached to the outer wall of the thin-walled container (3). The metal defect ground film (1) and the metal microstrip line film (2) are the same size. The upper edges of the metal defect ground film (1) and the metal microstrip line film (2) are flush with the opening edge of the thin-walled container (3). The metal defect ground film (1) and the metal microstrip line film (2) are attached to the inner and outer walls of the same part of the thin-walled container (3), and the lower edges of the two films are flush. The metal defect ground film (1) consists of a flexible dielectric substrate (5) and a metal reference ground (4) printed on the flexible dielectric substrate (5). Nested complementary open resonant rings NCSRR (10) are etched on the metal reference ground (4). The side of the metal defect ground film (1) without the metal reference ground is attached to the inner wall of the thin-walled container (3). The nested complementary open resonant ring NCSRR (10) is derived from the complementary open resonant ring CSRR and is used to improve the resonance characteristics of the microwave circuit of the sensor. The nested complementary open resonant ring NCSRR (10) is a dumbbell-shaped CSRR (21) symmetrical about the opening, which is nested inside a dumbbell-shaped open resonant ring SRR (22) of the same shape. The metal microstrip thin film (2) consists of a flexible dielectric substrate (7) and a U-shaped microstrip line (6) printed on the flexible dielectric substrate (7). The side of the metal microstrip thin film (2) without the microstrip line (6) is attached to the outer wall of the thin-walled container (3). The U-shaped microstrip line (6) is used to excite the NCSRR resonant unit to generate resonance; The transverse microstrip portion of the U-shaped microstrip line (6) is aligned with the opening portion of the NCSRR (10); and the opening ring is located at the center of the transverse portion of the U-shaped microstrip line.

2. A double-sided attached microwave sensor for detecting the dielectric constant of a liquid as described in claim 1, characterized in that, The two ends of the U-shaped microstrip line (6) are flush with one side edge of the flexible dielectric substrate (7). The two right-angle bends of the U-shaped microstrip line (6) are subjected to 45° external oblique cutting to ensure that the ratio of the distance from the 45° oblique cutting edge to the outer corner to the distance from the inner corner to the outer corner is 0.7~0.

8.

3. A double-sided attached microwave sensor for detecting the dielectric constant of a liquid as described in claim 1, characterized in that, The ring width of SRR (22) is taken as the ring width of CSRR (21). The opening distance of the SRR (22) is 1.5 to 3 times the opening distance of the CSRR (21).

4. A double-sided attached microwave sensor for detecting the dielectric constant of a liquid as described in claim 1, characterized in that, The distance between the lower edge of the NCSRR (10) and the lower edge of the metal reference ground (4) is more than 0.5 times the outer side length of the CSRR21.

5. A double-sided attached microwave sensor for detecting the dielectric constant of a liquid as described in claim 1, characterized in that, The sensor is a dual-port microwave resonant sensor. The two ports of the U-shaped microstrip line (6) are welded to the metal reference ground (4) and the female connector (11) of the radio frequency coaxial line through connector pins.

6. A double-sided attached microwave sensor for detecting the dielectric constant of a liquid as described in claim 1, characterized in that, The thin-walled container (3) is an open container of any shape with uniform sidewall thickness, and its wall thickness is 0.5mm~3mm.

7. A double-sided attached microwave sensor for detecting the dielectric constant of a liquid as described in claim 1, characterized in that, The thin-walled container (3) is made of glass, polypropylene, or silicone.

8. A double-sided attached microwave sensor for detecting the dielectric constant of a liquid as described in claim 1, characterized in that, The thickness of the flexible dielectric substrates (5) and (7) is between 0.01 mm and 0.1 mm, and the material is polyimide.

9. A double-sided attached microwave sensor for detecting the dielectric constant of a liquid as described in claim 1, characterized in that, The thickness of the metal reference ground (4) and the U-shaped microstrip line (6) is between 0.01 mm and 0.05 mm, and the material is copper, gold or tin.

10. A double-sided attached microwave sensor for detecting the dielectric constant of a liquid as described in claim 1, characterized in that, The vertical length of the U-shaped microstrip line (6) is more than 1 times the length of its horizontal portion, and the length of its horizontal portion is more than 1.5 times the outer side length of the NCSRR (10).

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