A coupled complementary spiral resonant sensor

Abstract

This invention relates to a coupled-complement spiral resonant sensor. The sensor includes: a microstrip line, a dielectric substrate, and a metal ground plane stacked sequentially from top to bottom; two mutually coupled circular complementary rotary resonators are etched on the metal ground plane; a sample of material under test is placed at the bottom of the metal ground plane, and the sample is positioned below the two circular complementary rotary resonators; when the sample interacts with an electric field energy to disrupt the field distribution, the resonant frequencies of the two circular complementary rotary resonators are obtained, and the thickness and dielectric constant of the sample are simultaneously measured based on the two resonant frequencies. This invention enables the simultaneous measurement of the thickness and dielectric constant of the sample, improving the sensor's sensitivity.

Description

Technical Field

[0001] This invention relates to the field of microwave sensor technology, and in particular to a coupled-complement spiral resonant sensor. Background Technology

[0002] Accurate measurement of the properties of dielectric materials has important applications in many fields, such as medicine, electronics, aerospace, and defense. Currently, the main measurement methods include the reflection method, transmission line method, and resonant cavity method. The reflection method generally measures thickness and dielectric constant over a wide frequency band by analyzing the phase and amplitude of the echo from the transmitting antenna; however, this method is generally costly and has low accuracy. The transmission line method typically places the dielectric material under test inside a transmission line (e.g., a waveguide) and obtains thickness and dielectric constant information by measuring transmission parameters. The resonant cavity method typically places the sample under test inside a resonant cavity and obtains thickness and dielectric constant information by measuring changes in the resonant frequency and quality factor. Both of these methods have high requirements for sample preparation, as the sample must be placed within a volume-constrained cavity, and non-destructive measurement is not easily achieved.

[0003] To address the aforementioned issues, in recent years, with the development of metamaterials technology, subwavelength planar microwave sensors have been widely used, providing an alternative method for measuring the electromagnetic properties of dielectric materials. Common single-resonator sensors cannot simultaneously measure the dielectric constant and thickness of the sample under test, and the sensitivity of single-resonator sensors is relatively low. Summary of the Invention

[0004] The purpose of this invention is to provide a coupled-complement spiral resonant sensor to solve the problem that single resonator sensors cannot simultaneously measure the dielectric constant and thickness of the material sample under test, and have low sensitivity.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] A coupled-complement spiral resonant sensor includes: a microstrip line, a dielectric substrate, and a metal ground plane stacked from top to bottom;

[0007] Two mutually coupled circular complementary rotary resonators are etched on the metal ground plane; the material sample to be tested is placed at the bottom of the metal ground plane, and the material sample to be tested is located below the two circular complementary rotary resonators;

[0008] When the field distribution is disturbed by the interaction between the test material sample and the electric field energy, the resonant frequencies of the two circular complementary rotating resonators are obtained, and the thickness and dielectric constant of the test material sample are simultaneously measured based on the two resonant frequencies.

[0009] Optionally, the circular complementary rotary resonator is formed by spiraling a metal wire.

[0010] Optionally, the quality factor Q and test frequency of the coupled complementary helical resonator can be adjusted by changing the outer diameter of the circular complementary rotary resonator, the spacing between adjacent metal wires, the width of the metal wires, and the gap between the two circular complementary rotary resonators.

[0011] Optionally, the electric field is concentrated in the gap between the two circular complementary rotating resonators.

[0012] Optionally, the relationship between the resonant frequency measurement and the thickness and dielectric constant of the material sample under test is as follows:

[0013] f L (ε d ,t)=3.086-0.2836ε d +0.0155ε d 2 +(0.2836ε d -0.0155ε d 2 )e -t / 0.1483

[0014] f H (ε d ,t)=3.248-0.317ε d +0.0181ε d 2 +(0.317ε d -0.0181ε d 2 )e -t / 0.1353

[0015] Among them, f L f is the lower of the two resonant frequencies; H f is the higher of the two resonant frequencies; L (ε d ,t) is the lower of the two resonant frequencies with respect to ε. d A function of t; f H (ε d ,t) is the higher of the two resonant frequencies with respect to ε. d A function of t; ε d t is the difference between the dielectric constant of the material sample and the dielectric constant of air; t is the thickness of the material sample.

[0016] Optionally, the two ends of the microstrip line are connected to SMA connectors. During measurement, the microstrip line is connected to a vector network analyzer through the SMA connectors. The vector network analyzer is used to analyze the two resonant frequencies and simultaneously measure the thickness and dielectric constant of the material sample under test.

[0017] Optionally, the characteristic impedance of the microstrip line is 50 ohms.

[0018] Optionally, the material of the dielectric substrate is Teflon.

[0019] According to specific embodiments provided by the present invention, the following technical effects are disclosed: The present invention provides a coupled complementary spiral resonant sensor, which employs two circular complementary spiral resonators coupled together. Their electromagnetic coupling can be equivalent to mutual capacitance and mutual inductance, thus enabling the sensor to have two resonant frequencies. When a sample to be measured is loaded, the two resonant frequencies change simultaneously, thereby allowing for simultaneous measurement of thickness and dielectric constant. Furthermore, compared to the single resonator case, the addition of coupling increases the resonant frequency shift of the sensor, thereby further improving the sensor's sensitivity. Attached Figure Description

[0020] 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.

[0021] Figure 1 This is a side view of the coupled complementary spiral resonator sensor provided by the present invention.

[0022] Figure 2 This is a top view of the coupled complementary spiral resonator sensor provided by the present invention;

[0023] Figure 3 A schematic diagram of the circular complementary spiral resonator provided by the present invention;

[0024] Figure 4 The equivalent circuit diagram of the circular complementary spiral resonator sensor provided by the present invention is shown below.

[0025] Figure 5 Simulation diagrams of the transmission parameters S21 under different dielectric constants obtained from modeling and simulation for this invention;

[0026] Figure 6 Simulation diagram of transmission parameters S21 under different thicknesses obtained from modeling and simulation of this invention;

[0027] Figure 7 f obtained from modeling and simulation for this invention L Relationship between dielectric constant and thickness;

[0028] Figure 8 f obtained from modeling and simulation for this invention HRelationship between dielectric constant and thickness. Detailed Implementation

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0030] The purpose of this invention is to provide a coupled-complement spiral resonant sensor that can simultaneously measure the thickness and dielectric constant of a sample of material under test, and further improves the sensitivity of the sensor.

[0031] 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.

[0032] Figure 1 This is a side view of the coupled-complement spiral resonator sensor provided by the present invention. Figure 2 This is a top view of the coupled complementary spiral resonator sensor provided by the present invention, as shown below. Figures 1-2 As shown, a coupled complementary spiral resonator sensor includes: a microstrip line 1, a dielectric substrate 2, and a metal ground plane 3 stacked sequentially from top to bottom; two mutually coupled circular complementary spiral resonators 4 are etched on the metal ground plane 3; a material sample to be tested is placed at the bottom of the metal ground plane 3, and the material sample to be tested is positioned below the two circular complementary spiral resonators 4; when the material sample to be tested interacts with the electric field energy to disturb the field distribution, the resonant frequencies of the two circular complementary spiral resonators 4 are obtained, and the thickness and dielectric constant of the material sample to be tested are simultaneously measured based on the two resonant frequencies.

[0033] In practical applications, the microstrip line 1 is positioned directly above the center of the dielectric substrate 2, and the metal ground plane 3 is positioned directly below the dielectric substrate 2. Two circular complementary spiral resonators 4 are etched in the center of the metal ground plane 3 and pass below the microstrip line 1. SMA connectors are placed at both ends of the microstrip line, which are connected to a vector network analyzer during measurement. The vector network analyzer is used to analyze the two resonant frequencies and simultaneously measure the thickness and dielectric constant of the material sample under test. Figure 2 The width of the microstrip line 1 is W; the thickness of the microstrip line 1 and the metal ground plane 3 are selected from commonly used thicknesses on the market.

[0034] Figure 3 A schematic diagram of the circular complementary spiral resonator provided by the present invention is shown below. Figure 3As shown, the circular complementary spiral resonator 4 is formed by spiraling a metal wire.

[0035] In practical applications, the size parameters of the circular complementary spiral resonator 4 are determined by simulation optimization and taking into account the manufacturing precision. The upper and lower parts of the spiral resonator are each composed of a set of concentric semicircular metal wires, with different centers of the two parts, and the metal wires are connected at the left end.

[0036] By changing the outer diameter L of the circular complementary spiral resonator 4 R The quality factor Q and test frequency of the coupled complementary spiral resonator sensor are adjusted by considering the spacing s between adjacent metal wires, the width w of the metal wire, and the gap d between the two circular complementary spiral resonators 4, combined with the precision during processing.

[0037] This invention utilizes a planar sensor structure to characterize the thickness of the sample under test. This measurement method is based on field perturbation; when the material under test interacts with the stored magnetic and electric field energy, thereby disrupting the field distribution, the resonant frequency of the resonant structure will change. The circular complementary helical resonator 4 used in this invention can provide a strong electric field between the gaps in the metal wires, thus generating greater sensitivity. This invention uses a vector network analyzer to measure the change in the resonant frequency after the sensor is applied to the sample under test, thereby determining the dielectric constant and thickness of the medium under test.

[0038] In practical applications, the electric field is concentrated in the gap between the two circular complementary helical resonators 4.

[0039] In practical applications, the thickness of the dielectric substrate 2 is optimized based on a combination of measurement sensitivity and manufacturing cost, and the material used is Teflon. The characteristic impedance of the microstrip line 1 is 50 ohms to achieve matching.

[0040] Figure 4 This is the equivalent circuit diagram of the sensor corresponding to the present invention. When the electrical size of the resonator is sufficiently small, its electromagnetic response can be described using a lumped circuit model. C c1 and C c2 These represent the coupling capacitances between microstrip line 1 and the two resonators, respectively; L r and C r These are the equivalent inductance and capacitance of the spiral resonator itself; the electrical and magnetic coupling between the two resonators is caused by the mutual capacitance C in the equivalent circuit. M And mutual inductance M represents; P1 is the first port of the equivalent circuit; R1 is the equivalent resistance of the microstrip line; P2 is the second port of the equivalent circuit; Rr is the equivalent resistance of the resonator.

[0041] Thus, two resonant branches can generate two resonant points. As the distance between the two resonators increases, the mutual capacitance and mutual inductance decrease. The situation is the same as with a single resonator when there is no coupling. The mutual capacitance can be represented as a Π-shaped circuit between the two branches. When a sample is placed on the sensor, the sample causes a change in capacitance Cr. At this time, the resonant frequency f affects the capacitance C. r The derivative of the first case is greater than that of the uncoupled case, thus increasing the sensor's sensitivity.

[0042] The circular complementary helical resonator 4 used in this invention, compared to the commonly used CSRR (complementary open-circuit resonator), can concentrate the electric field more within the resonator's gap. When the sample under test causes a small disturbance to the resonator's electric field, higher sensitivity can be achieved. Furthermore, compared to other shapes, the circular resonator can achieve a higher equivalent capacitance while the equivalent inductance changes relatively little, resulting in a higher quality factor Q value, thereby improving measurement accuracy.

[0043] This invention utilizes full-wave simulation software to model and simulate a sensor of a defined size. For example... Figure 5 As shown, where ε r Let f be the dielectric constant of the material sample to be tested. With a sample thickness of 1 mm, this invention obtains simulation diagrams of the transport parameters S21 under different dielectric constants. When the dielectric constant remains constant, f... L and f H The resonant frequency decreases with increasing thickness. When the thickness reaches 1 mm, the change in resonant frequency is relatively small. A higher relative permittivity of the sample increases the sensitivity to thickness measurement. Furthermore, keeping the thickness constant, f... L and f H The sensitivity of the resonant frequency to the dielectric constant also decreases as the dielectric constant increases. When the thickness of the sample is large, the sensitivity of the resonant frequency to the dielectric constant is also large. It can be seen that when the thickness of the sample is 1 mm, as the dielectric constant changes from 1 to 10, the shift between the two resonant frequencies can reach 1.406 GHz and 1.516 GHz, respectively. The average shift for each change of 1 in the dielectric constant is 156 MHz and 168 MHz, indicating high sensitivity.

[0044] like Figure 6 As shown, when the sample under test is FR4 dielectric (relative permittivity 4.5), the present invention obtains the transmission parameter S21 simulation diagram under different thicknesses. When the thickness varies from 0.1 mm to 1 mm, the offset of the two resonant frequencies is 372 MHz and 404 MHz, and the average offset caused by each 0.1 mm thickness is 41.3 MHz and 44.9 MHz, respectively, indicating high sensitivity.

[0045] Figure 7 and Figure 8This diagram illustrates the relationship between the two resonant frequencies of this invention and the dielectric constant and thickness. To derive the thickness and dielectric constant of the sample from the resonant frequency, a mathematical model is needed to establish their relationship. In this invention, the relationship between the resonant frequency and the dielectric constant of the medium under test can be expressed as a quadratic function, and the relationship with the thickness can be expressed as an exponential function. Furthermore, when the relative dielectric constant of the sample under test is 1 or the thickness is 0, the resonant frequency should be equal to the unloaded resonant frequency. Based on data fitting, the relationship between the resonant frequency and the thickness and dielectric constant can be obtained as follows:

[0046] f L (ε d ,t)=3.086-0.2836ε d +0.0155ε d 2 +(0.2836ε d -0.0155ε d 2 )e -t / 0.1483

[0047] f H (ε d ,t)=3.248-0.317ε d +0.0181ε d 2 +(0.317ε d -0.0181ε d 2 )e -t / 0.1353

[0048] Among them, f L f is the lower of the two resonant frequencies; H f is the higher of the two resonant frequencies; L (ε d ,t) is the lower of the two resonant frequencies with respect to ε. d A function of t; f H (ε d ,t) is the higher of the two resonant frequencies with respect to ε. d The dielectric constant of the sample is a function of t; t is the difference between the dielectric constant of the sample and the dielectric constant of air; and t is the thickness of the sample.

[0049] Based on the above formula, when using the present invention to measure relative permittivity and thickness, the sample to be tested can be placed under two helical resonators and completely covered by them; the permittivity and thickness of the sample to be tested can be calculated by the offset of the two resonant frequencies of the sensor.

[0050] The experimental process of this invention is simple, the sample preparation requirements are low, and the testing is easy.

[0051] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0052] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A coupled-complement spiral resonant sensor, characterized in that, include: The microstrip line, dielectric substrate, and metal ground plane are stacked sequentially from top to bottom; Two mutually coupled circular complementary rotary resonators are etched on the metal ground plane; The circular complementary rotary resonator is formed by spiraling a metal wire; the bottom of the metal ground plane is where the material sample to be tested is placed, and the material sample to be tested is located below the two circular complementary rotary resonators; When the field distribution is disturbed by the interaction between the test material sample and the electric field energy, the resonant frequencies of the two circular complementary rotating resonators are obtained, and the thickness and dielectric constant of the test material sample are simultaneously measured based on the two resonant frequencies. The relationship between the resonant frequency measurement and the thickness and dielectric constant of the material sample under test is as follows: in, The lower of the two resonant frequencies; The higher of the two resonant frequencies; The lower of the two resonant frequencies is related to The function; The higher of the two resonant frequencies is related to The function; This is the difference between the dielectric constant of the material sample and the dielectric constant of air; The thickness of the material sample to be tested; The electric field is concentrated in the gap between the two circular complementary rotary resonators; the quality factor Q and test frequency of the coupled complementary spiral resonator are adjusted by changing the outer diameter of the circular complementary rotary resonators, the spacing between adjacent metal wires, the width of the metal wires, and the gap between the two circular complementary rotary resonators.

2. The coupled-complement spiral resonant sensor according to claim 1, characterized in that, The two ends of the microstrip line are connected to SMA connectors. During measurement, the microstrip line is connected to a vector network analyzer through the SMA connectors. The vector network analyzer is used to analyze the two resonant frequencies and simultaneously measure the thickness and dielectric constant of the material sample under test.

3. The coupled-complement spiral resonant sensor according to claim 1, characterized in that, The characteristic impedance of the microstrip line is 50 ohms.

4. The coupled-complement spiral resonant sensor according to claim 1, characterized in that, The substrate material is Teflon.

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