A high-sensitivity microwave sensor for measuring the dielectric constant of a material

Abstract

The present application belongs to the field of microwave measurement and sensing technology, and particularly relates to a high-sensitivity microwave sensor for measuring material dielectric constant, comprising a composite plate, the top surface of the composite plate is provided with a transmission part, the bottom surface of the composite plate is provided with a groove, an electric field is formed between the transmission part and the groove, a plurality of metal through holes for preventing electric field energy leakage are formed on the composite plate, the plurality of metal through holes are symmetrically arranged on both sides of the transmission part and distributed around the groove, the plurality of metal through holes are arranged as a resonance area, and the resonance area is used for placing a to-be-measured object and located on the top surface of the composite plate. The present application can realize miniaturization, low cost and high-precision dielectric constant measurement, and is suitable for measuring the dielectric constant value of high-frequency plate materials used in microwave circuits.

Description

Technical Field

[0001] This invention belongs to the field of microwave measurement and sensing technology, and particularly relates to a high-sensitivity microwave sensor for measuring the dielectric constant of materials. Background Technology

[0002] The dielectric constant is an important parameter characterizing the electrical properties of dielectric materials. In microwave circuits, the dielectric constant of the circuit substrate affects the signal transmission rate and also determines the characteristic impedance of the circuit. Accurate measurement of the dielectric constant is helpful for accurate modeling and design of electromagnetic systems. Traditional methods for measuring the dielectric constant are limited by the complexity of the measuring equipment and the high cost of testing, making the measurement process cumbersome and expensive.

[0003] In recent years, microwave sensors have been widely used in biomedicine, concentration detection, and solid and liquid mass testing due to their advantages such as real-time measurement, non-destructive operation, and low cost. Many researchers have chosen to use the microwave plane resonance method to measure the dielectric constant of materials. The plane resonance method is simple to measure, easy to fabricate, and has high measurement accuracy. When the object to be measured is placed in the resonant region, the electric field in the resonant region will be disturbed, which will cause a shift in the resonant frequency. The dielectric constant value of the object to be measured can be obtained by observing the change in the resonant frequency.

[0004] Sreedevi P. Chakyar et al. proposed a microwave sensor using a split-ring resonator (SRR) metamaterial structure to measure the dielectric constant of materials, but the measurement accuracy was not high. The literature Yeo J, Lee JI. Meander-LineSlot-Loaded High-Sensitivity Microstrip Patch Sensor Antenna for Relative Permittivity Measurement[J]. Sensors, 2019, 19(21): 4660-4675. describes a high-sensitivity microstrip patch sensor with a loaded curved groove structure, which has higher sensitivity than the traditional rectangular patch structure, but the sample size is relatively large. Therefore, sample miniaturization and high-precision measurement have become difficult problems to be solved in current technology. Summary of the Invention

[0005] The purpose of this invention is to provide a high-sensitivity microwave sensor for measuring the dielectric constant of materials, so as to solve the above-mentioned problems and achieve the goal of low-cost, fast and accurate measurement of material properties.

[0006] To achieve the above objectives, the present invention provides the following solution: a high-sensitivity microwave sensor for measuring the dielectric constant of materials, comprising a composite plate, wherein a transmission section is provided on the top surface of the composite plate, and a groove is formed on the bottom surface of the composite plate, wherein an electric field is formed between the transmission section and the groove, and a plurality of metal through holes are provided on the composite plate to prevent leakage of electric field energy, the plurality of metal through holes are symmetrically arranged on both sides of the transmission section and distributed around the groove, and a resonant region is formed between the plurality of metal through holes, wherein the resonant region is used to place the object to be measured and is located on the top surface of the composite plate.

[0007] Preferably, the groove includes a first square groove and a second square groove located inside the first square groove. A first notch is provided at the middle of one side of the first square groove, and the first notch extends to the inner side of the first square groove. A second notch is provided at the middle of one side of the second square groove near the first notch, and part of the first notch extends into the second notch. A gap is provided between the first square groove and the second square groove. The transmission part is located above the first notch and the second notch.

[0008] Preferably, the transmission unit includes a metal transmission line disposed on the top surface of the composite plate, with SMA connectors connected to both ends of the metal transmission line. The two SMA connectors are fixedly connected to opposite sides of the composite plate, and the metal transmission line is vertically aligned with the first notch.

[0009] Preferably, the composite board includes an FR4 substrate and a copper clad layer fixedly connected to the bottom surface of the FR4 substrate, the groove is formed on the copper clad layer, and a plurality of the metal through holes simultaneously penetrate the FR4 substrate and the copper clad layer.

[0010] Preferably, the length c of the outer side of the first square groove away from the first notch is 10-15mm, the length b of the inner side of the first square groove adjacent to the first notch is 7-12mm, the length a of the first notch is 2-7mm, the width d of the first square groove is 0.8-1.3mm, and the gap g between the first notches is 1.5-2.5mm.

[0011] Preferably, the distance between the second notch and the second notch on the second square groove is 4-9 mm, the length e of the inner side of the second square groove adjacent to the second notch is 2-7 mm, and the groove width d of the second square groove is 0.8-1.3 mm.

[0012] Preferably, the inner diameter R of the metal through-hole is 1.4-1.6 mm, the gap between adjacent metal through-holes is no greater than 1 mm, and the length distance L of a plurality of metal through-holes along the transmission direction of the transmission section is... S =13.5-18.5mm.

[0013] Preferably, the linewidth W of the metal transmission line P =1.3mm.

[0014] Preferably, the side dimension of the top surface of the composite plate along the transmission direction is L = (15.5-21.5) cm, and the side dimension of the top surface of the composite plate perpendicular to the transmission direction is W = (30-35) cm.

[0015] The present invention has the following technical advantages: After an electric field is formed between the transmission part and the groove, a resonant region can be formed under the action of several metal through holes. When the object to be tested is placed in the resonant region, the resonant frequency of the object to be tested can be obtained. By comparing it with the resonant frequency when the sensor is unloaded, the sensitivity of the sensor to changes in dielectric constant can be determined. Based on this and through the obtained empirical relationship, the feasibility of the sensor in measuring the dielectric constant of different materials can be proved. Several metal through holes can prevent energy leakage near the object to be tested. The sensor of this application can obtain higher measurement accuracy and sensitivity, and has a simple structure, saves costs, and is easy to operate. It is suitable for rapidly measuring the dielectric constant of high-frequency board materials used in microwave circuits and has high application prospects in the field of microwave circuit manufacturing. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the main structure of the sensor of the present invention;

[0018] Figure 2 This is a schematic diagram of the metal transmission line structure of the present invention;

[0019] Figure 3 This is a schematic diagram of the copper-clad layer structure of the present invention;

[0020] Figure 4 This is a schematic diagram of the groove structure of the present invention;

[0021] Figure 5 This is a diagram showing the resonant frequency of the sensor under no-load conditions according to the present invention.

[0022] Figure 6 This is a diagram showing the resonant frequencies of the loading material when the dielectric constant is between 1 and 10.

[0023] Figure 7 This is a fitted curve of the dielectric constant of the material of this invention and the resonant frequency of the sensor;

[0024] Figure 8 The diagram shows the resonant frequencies of five common high-frequency substrates when the present invention is loaded.

[0025] Figure 9 This is a graph showing the resonant frequency and fitting curve matching when five types of plates are loaded in this invention.

[0026] Among them, 1. Metal transmission line; 2. FR4 substrate; 3. Metal through hole; 4. SMA connector; 5. Measurement area; 6. Groove; 601. First square groove; 6011. First notch; 602. Second square groove; 6021. Second notch; 7. Copper cladding layer. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] Reference Figure 1-4 As shown, the present invention provides a high-sensitivity microwave sensor for measuring the dielectric constant of materials, including a composite plate. A transmission section is provided on the top surface of the composite plate, and a groove 6 is formed on the bottom surface of the composite plate. An electric field is formed between the transmission section and the groove 6. A plurality of metal through holes 3 are formed on the composite plate to prevent leakage of electric field energy. The plurality of metal through holes 3 are symmetrically arranged on both sides of the transmission section and distributed around the groove 6. The plurality of metal through holes 3 are set as a resonant region. The resonant region is used to place the object to be measured and is located on the top surface of the composite plate.

[0030] After an electric field is formed between the transmission section and the groove 6, a resonant region can be formed under the action of several metal through holes 3. At this time, the object to be measured is placed in the resonant region, and the resonant frequency of the object to be measured can be obtained. By comparing it with the resonant frequency when the sensor is unloaded, the sensitivity of the sensor to changes in dielectric constant can be determined. Based on this and through the obtained empirical relationship, the feasibility of the sensor to measure the dielectric constant of different materials can be proved. Several metal through holes 3 can prevent energy leakage near the object to be measured. The sensor of this application can obtain higher measurement accuracy and sensitivity, and has a simple structure, saves costs, and is easy to operate. It is suitable for rapidly measuring the dielectric constant of high-frequency board materials used in microwave circuits and has a high application prospect in the field of microwave circuit manufacturing.

[0031] In a further optimized design, the groove 6 includes a first square groove 601 and a second square groove 602 located inside the first square groove 601. A first notch 6011 is formed at the middle of one side of the first square groove 601, extending into the inner side of the first square groove 601. A second notch 6021 is formed at the middle of one side of the second square groove 602 near the first notch 6011, with a portion of the first notch 6011 extending into the second notch 6021. A gap is provided between the first square groove 601 and the second square groove 602. The transmission part is located above the first notch 6011 and the second notch 6021. The area between the first square groove 601 and the second square groove 602 is the measurement area 5.

[0032] Based on the structural relationship between the first notch 6011 and the second notch 6021, the structures on both sides of the notch are bent and extended inward, making the structure more compact and widening the range of the measurement area 5. This increases the contact area between the object to be measured and the sensor. At the same time, based on several metal through holes 3, the leakage of signal energy from the measurement area 5 is restricted, and the electric field is concentrated in the test area, enabling the sensor to achieve better measurement results. Thus, the highest electric field strength is obtained in the measurement area 5.

[0033] The scheme is further optimized, and the transmission unit includes a metal transmission line 1 disposed on the top surface of the composite plate. SMA connectors 4 are connected to both ends of the metal transmission line 1, and the two SMA connectors 4 are fixedly connected to opposite sides of the composite plate. The metal transmission line 1 is vertically aligned with the first notch 6011. The SMA connectors are used to connect to a vector network analyzer, on which S... 21 Parameters and transmission coefficient values.

[0034] A further optimized design includes an FR4 substrate 2 and a copper-clad layer 7 fixedly connected to the bottom surface of the FR4 substrate 2. Grooves 6 are formed in the copper-clad layer 7, and several metal through-holes 3 penetrate both the FR4 substrate 2 and the copper-clad layer 7. The FR4 substrate 2 is made of epoxy glass cloth laminate FR4, a low-cost material with good dielectric and electrical loss properties, and is widely used in electronic circuit manufacturing. A first square groove 601 and a second square groove 602 are etched on the copper-clad layer 7.

[0035] Further optimization of the scheme: the length of the outer side of the first square groove 601 away from the first notch 6011 is c = 12mm, the length of the inner side of the first square groove 601 adjacent to the first notch 6011 is b = 9mm, the length of the first notch 6011 is a = 4mm, the groove width of the first square groove 601 is d = 1mm, and the gap between the first notches 6011 is g = 1.5-2.5mm.

[0036] Further optimization of the scheme: the distance between the second notch 6021 on the second square groove 602 is 4-9mm, the length of the inner side of the second square groove 602 adjacent to the second notch 6021 is e=4mm, and the groove width of the second square groove 602 is d=1mm.

[0037] Further optimization of the scheme: the inner diameter R of the metal through-hole 3 is 1.6mm, the gap between adjacent metal through-holes 3 is no greater than 1mm, and the length distance L of several metal through-holes 3 along the transmission direction of the transmission section is... S =15.5mm. Metal through holes 3 are evenly distributed around the groove 6, with a certain interval between each metal through hole 3. This structure is used to limit energy leakage and concentrate the electric field in the measurement area 5, so that the sensor can achieve better measurement results.

[0038] Further optimization of the scheme: the linewidth W of metal transmission line 1 P =1.3mm, to match a 50-ohm port impedance.

[0039] Further optimization of the scheme: the side dimension of the top surface of the composite board along the transmission direction is L = (15.5-21.5) cm, and the side dimension of the top surface of the composite board perpendicular to the transmission direction is W = (30-35) cm.

[0040] The design was further optimized, and the thickness of the composite panel was reduced to 0.7mm.

[0041] The working process of this embodiment is as follows:

[0042] like Figure 5 It can be seen that the resonant frequency of the sensor is 2 GHz when no test material is loaded.

[0043] like Figure 6 The resonant frequency diagrams for the sensor material with dielectric constants of 1, 3, 5, 7, 9, and 10 correspond to resonant frequencies of 2 GHz, 1.82 GHz, 1.70 GHz, 1.60 GHz, 1.52 GHz, and 1.48 GHz, respectively. The total displacement from 2 GHz to 1.48 GHz is 520 MHz, demonstrating the sensor's high sensitivity to changes in dielectric constant.

[0044] like Figure 7 The relationship between the dielectric constant of the material and the resonant frequency of the sensor can be seen in the fitted curve. By fitting the dielectric constant of the material with the corresponding resonant frequency, an empirical formula for the relationship between the dielectric constant and the resonant frequency of the sensor is obtained:

[0045] ε' = 18.43(f r -1) 2 -44.6(f r -1)+27.17 (1)

[0046] Where ε' is the dielectric constant, f r It is the resonant frequency.

[0047] like Figure 8 The resonant frequency diagram of the sensor after loading the material sample is shown. Five commonly used high-frequency boards in microwave circuits were selected: Rogers5880, Rogers4003, FR4, RF-60, and Rogers3010.

[0048] The five selected test materials—Rogers 5880, Rogers 4003, FR4, RF-60, and Rogers 3010—have dielectric constants of 2.2, 3.55, 4.4, 6.15, and 10.2, respectively. After being applied to the test area, the corresponding resonant frequencies are 1.88 GHz (Rogers 5880), 1.78 GHz (Rogers 4003), 1.72 GHz (FR4), 1.64 GHz (RF-60), and 1.46 GHz (Rogers 3010).

[0049] Substituting the above data into the empirical formula ε' = 18.43(f r -1) 2 -44.6(f r The verification was performed in -1)+27.17. The error values ​​of the measurement results of the five types of boards were 0.45%, 1.27%, 0.22%, 0.32%, and 1.76%, respectively, with an average error value of 0.8%.

[0050] like Figure 9 It can be seen that the results have a very high degree of matching with the empirical formula, which well proves the feasibility of using this sensor to measure the dielectric constant of materials.

[0051] This invention provides a high-sensitivity microwave sensor for measuring the dielectric constant of materials. By placing the material under test in the measurement area and connecting one end of the sensor to a vector network analyzer to read the resonant frequency data, the dielectric constant of the loaded sample is calculated using empirical formulas obtained from previous experiments. Experiments have demonstrated that this sensor has excellent reliability. Compared with other sensors, this invention offers higher measurement accuracy and sensitivity, lower manufacturing cost, simpler operation, and smaller sample size. It is suitable for rapidly measuring the dielectric constant of high-frequency substrates used in microwave circuits and has high application prospects in the field of microwave circuit manufacturing.

[0052] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention, and are not intended to 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 therefore should not be construed as a limitation of this invention.

[0053] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A high-sensitivity microwave sensor for measuring the dielectric constant of materials, characterized in that: The composite plate includes a transmission section on its top surface and a groove (6) on its bottom surface. An electric field is formed between the transmission section and the groove (6). The composite plate has several metal through holes (3) to prevent leakage of electric field energy. The several metal through holes (3) are symmetrically arranged on both sides of the transmission section and distributed around the groove (6). The several metal through holes (3) are set as a resonant region. The resonant region is used to place the test item and is located on the top surface of the composite plate. The groove (6) includes a first square groove (601) and a second square groove (602) located inside the first square groove (601). A first notch (6011) is provided at the middle of one side of the first square groove (601), and the first notch (6011) extends to the inside of the first square groove (601). A second notch (6021) is provided at the middle of one side of the second square groove (602) near the first notch (6011), and part of the first notch (6011) extends into the second notch (6021). A gap is provided between the first square groove (601) and the second square groove (602). The transmission part is located above the first notch (6011) and the second notch (6021). The length c of the outer side of the first square groove (601) away from the first notch (6011) is 10mm~15mm, the length b of the inner side of the first square groove (601) adjacent to the first notch (6011) is 7mm~12mm, the length a of the first notch (6011) is 2mm~7mm, the groove width d of the first square groove (601) is 0.8mm~1.3mm, and the gap g between the first notches (6011) is 1.5mm~2.5mm. The distance between the second notch (6021) on the second square groove (602) is 4mm~9mm, the length e of the inner side of the second square groove (602) adjacent to the second notch (6021) is 2mm~7mm, and the groove width d of the second square groove (602) is 0.8mm~1.3mm.

2. The high-sensitivity microwave sensor for measuring the dielectric constant of materials according to claim 1, characterized in that: The transmission unit includes a metal transmission line (1) disposed on the top surface of the composite plate. Both ends of the metal transmission line (1) are respectively connected to SMA connectors (4). The two SMA connectors (4) are respectively fixedly connected to opposite sides of the composite plate. The metal transmission line (1) is vertically aligned with the first notch (6011).

3. The high-sensitivity microwave sensor for measuring the dielectric constant of materials according to claim 1, characterized in that: The composite board includes an FR4 substrate (2) and a copper clad layer (7) fixedly connected to the bottom surface of the FR4 substrate (2). The groove (6) is formed on the copper clad layer (7), and a plurality of metal through holes (3) simultaneously penetrate the FR4 substrate (2) and the copper clad layer (7).

4. The high-sensitivity microwave sensor for measuring the dielectric constant of materials according to claim 1, characterized in that: The inner diameter R of the metal through hole (3) is 1.4mm~1.6mm, the gap between adjacent metal through holes (3) is no more than 1mm, and the length distance LS of several metal through holes (3) along the transmission direction of the transmission section is 13.5mm~18.5mm.

5. The high-sensitivity microwave sensor for measuring the dielectric constant of materials according to claim 2, characterized in that: The line width WP of the metal transmission line (1) is 1.3mm.

6. The high-sensitivity microwave sensor for measuring the dielectric constant of materials according to claim 3, characterized in that: The side dimension L of the top surface of the composite plate along the transmission direction is 15.5cm to 21.5cm, and the side dimension W of the top surface of the composite plate perpendicular to the transmission direction is 30cm to 35cm.

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