CN220154547U - Microwave sensor for measuring complex dielectric constant of liquid - Google Patents

Abstract

The utility model discloses a microwave sensor for measuring complex dielectric constant of liquid, which at least comprises a dielectric plate, a resonator arranged on the upper layer of the dielectric plate, a signal input microstrip line and a signal output microstrip line which are electrically connected with the resonator, and a PDMS fluid channel arranged on the resonator, wherein the signal input microstrip line is provided with a port 1 for inputting a measurement signal; the resonator is used for generating a resonance signal according to an input signal, wherein a modified SRR structure is adopted as a sensing area to provide a basic resonance signal, and the resonance signal has corresponding resonance frequency and resonance depth under the disturbance of liquids with different dielectric constants; the PDMS fluid channel is used for stably injecting liquid to be detected with different dielectric constants into the sensing area; the signal output microstrip line is provided with a port 2 for outputting a resonance signal, and the resonance frequency and the resonance depth generated by the liquid to be measured are obtained through the resonance signal, so that the complex dielectric constant of the liquid to be measured is obtained.

Description

Microwave sensor for measuring complex dielectric constant of liquid

Technical Field

The utility model relates to the field of microwave radio frequency sensing, in particular to a microwave sensor for measuring complex dielectric constants of liquid.

Background

The microwave sensor measurement technology has the advantages of non-invasiveness, high sensitivity, high measurement precision, low manufacturing and measurement cost and the like, and has great potential in wide application in the fields of mechanical displacement characterization, rotation angle characterization, complex dielectric constant characterization and the like. For example, a planar microfluidic sensor for measuring complex dielectric constants of liquids is based on the measurement principle that when liquids to be measured with different complex dielectric constants are added into a fluid channel above a resonator, the liquids to be measured change the dielectric properties of the resonator, so that the resonant frequency and the resonant depth change, and the complex dielectric constants of the liquids to be measured can be reversely represented by extracting the change of resonant parameters of the resonator.

Currently, the design of planar microfluidic sensors based on stepped impedance resonator (Stepped impedance resonator, SIR) structures, complementary split ring resonator (Complementary Spit Ring Resonator, CSRR) structures has become a popular topic in recent years. Compared with other types of microwave measuring sensors, the planar sensor has the advantages of easy manufacture and easy integration on a radio frequency chip. In addition, the microwave microfluidic sensor does not need a labeling protocol or a biological label, so that a large amount of reagent, solution and time are not consumed for researching liquid chemicals or biological liquids, and the cost for extracting liquid parameters is greatly reduced.

However, most of the microwave sensors currently developed use a CSRR structure and an SIR structure. In this case, the electric field distribution of SIR structure is not concentrated, so that more liquid sample is required for each measurement, and thus it is difficult to perform noninvasive measurement in practice. While the CSRR structure uses a coupling form in transmission, although the electric field is relatively concentrated, this has an effect on sensitivity. In practical applications, however, the sensitivity requirements for measurement are high, because the accuracy requirements of chemistry and biology itself on the concentration of the liquid are extremely high. In addition, the non-invasiveness of the sensor is also a very important indicator. The loss of excess liquid to be measured during measurement is certainly a great waste for the industry.

Therefore, in view of the defects existing in the prior art, it is necessary to perform research to realize a high-quality microwave sensor with non-invasiveness, high sensitivity and low manufacturing and measuring cost, so that the high-quality microwave sensor can generate value in practical application.

Disclosure of Invention

In order to overcome the defects in the prior art, the utility model provides a microwave sensor for measuring the complex dielectric constant of liquid, and provides an improved SRR structure based on an open split ring resonator (split ring resonator, SRR) to realize a microfluidic noninvasive measurement sensor.

In order to solve the prior art difficulty, the technical scheme of the utility model is as follows:

the microwave sensor for measuring the complex dielectric constant of the liquid at least comprises a dielectric plate, a resonator arranged on the upper layer of the dielectric plate, a signal input microstrip line and a signal output microstrip line which are electrically connected with the resonator, and a PDMS fluid channel arranged on the resonator, wherein the signal input microstrip line is provided with a port 1 for inputting a measurement signal; the resonator is used for generating a resonance signal according to an input signal, wherein a modified SRR structure is adopted as a sensing area to provide a basic resonance signal, and the resonance signal has corresponding resonance frequency and resonance depth under the disturbance of liquids with different dielectric constants; the PDMS fluid channel is used for stably injecting liquid to be detected with different dielectric constants into the sensing area; the signal output microstrip line is provided with a port 2 for outputting a resonance signal, and the resonance frequency and the resonance depth generated by the liquid to be measured are obtained through the resonance signal, so that the complex dielectric constant of the liquid to be measured is obtained.

As a further improvement scheme, the improved SRR structure at least comprises a capacitor plate, an interdigital capacitor, an open outer ring and an open inner ring, wherein one side of the open outer ring is provided with a gap, two opposite capacitor plates are arranged at the gap and are respectively and directly electrically connected with a signal input microstrip line and a signal output microstrip line, and the interdigital capacitor is arranged between the two capacitor plates.

As a further improvement, the PDMS fluid channel is disposed directly above the interdigital capacitor.

As a further improvement scheme, the PDMS fluid channel is made of polydimethylsiloxane material and is in a cuboid structure, and comprises PDMS colloid, a fluid channel empty groove and an inlet and outlet cylindrical injection port.

As a further improvement, the lower layer of the dielectric plate is provided with a defected ground structure, and metal right below the improved SRR structure is removed so as to avoid capacitance generated between the improved SRR structure and the ground plane.

As a further improvement, the distance between the open inner ring and the open outer ring in the modified SRR structure is greater than 0.5mm.

As a further development, the defective ground structure has a metal of 10mm length and 9mm width in the midpoint of the ground plane cut out.

As a further development, the fluid channel produced is a curved, folded cuboid with a cross-sectional area of 0.15mm×0.2mm and a total length of the fluid channel of 17mm.

As a further improvement, the improved SRR structure forms a resonant circuit, the resonant frequency of which depends on the inductance and capacitance of the overall improved SRR structure, and the specific expression is as follows:

when the liquid to be measured is added into the fluid channel, the overall resonant frequency of the resonant circuit changes, wherein the capacitance part is not completely dependent on the capacitance of the improved SRR structure, and the capacitance of the liquid to be measured is related to the capacitance of the liquid to be measured, and the specific expression is as follows:

wherein L is _p 、C _p Respectively representing the inductance and capacitance of the improved SRR structure; c (C) _LUT Simulating a change in sensor capacitance when the liquid to be measured is added to the sensor;

the sensor sensitivity is defined as:

wherein Δf _z Is the shift in resonant frequency, delta epsilon is the change in dielectric constant of the dielectric sample loaded on the resonator; when the liquid to be measured is loaded into the fluid channel, it is equivalent to adding an additional capacitor C to the sensor _LUT The method comprises the steps of carrying out a first treatment on the surface of the The above formula can be used to obtain:

wherein Δεand C _LUT Is determined by the physical characteristics of the measured liquid, f _z And C _p Determined only by the physical characteristics of the sensor; through f _z And C _p Is the control sensitivity; when f _z And C _p When increased, the sensitivity also increases.

As a further improvement, the SRR structure is modified as a sensing area, provides basic resonance, and changes its own resonance frequency and depth under the disturbance of liquids with different dielectric constants, and the PDMS fluid channel is used for stably injecting liquids to be measured with different dielectric constants into the sensing area. And acquiring sensing information through resonance frequencies and resonance depths generated by different liquids to be detected so as to extract the complex dielectric constant of the liquid sample.

The PDMS fluid channel comprises PDMS colloid, a fluid channel empty slot and an in-out cylindrical injection port;

the signal input microstrip line and the signal output microstrip line are directly connected with the improved SRR structure and are used for accessing signals and outputting signals;

the defected ground structure removes metal directly below the modified SRR structure at the conventional ground plane, avoiding capacitance generated between the modified SRR structure and the ground plane, and thus reducing the sensitivity of the sensor.

As a further improvement scheme, the material of the fluid channel adopts polydimethylsiloxane, and the structure is cuboid and consists of colloid, a micro-fluid channel and a cylindrical hollow groove.

As a further improvement, the distance between the open inner ring and the open outer ring of the improved SRR structure should be greater than 0.5mm, avoiding electromagnetic coupling.

As a further improvement, the defected ground structure digs out the metal with the length of 10mm and the width of 9mm at the center on the ground plane so as to avoid the generation of interference capacitance between the improved SRR structure and the ground plane metal.

As a further improvement scheme, the improved SRR structure is printed on the upper layer of the dielectric plate, the outer ring of the improved SRR structure is added with the capacitor plate and the interdigital capacitor structure, and the inner ring of the improved SRR structure adopts a traditional rectangular structure, so that the position is adjusted in aspects, and the electric field is more concentrated.

As a further improvement, the signal input microstrip line is directly connected with the capacitor plate of the improved SRR structure, wherein the width of the signal input microstrip line should be smaller than the width of the capacitor plate to ensure good access of the signal.

As a further development, the fluid channel can be regarded as a bent cuboid, the total length of which is 17mm, the height of the fluid channel is 0.2mm, and the width is 1mm.

As a preferred technical solution, the signal input microstrip line is directly connected with the capacitor plate of the improved SRR structure.

As a preferable technical scheme, the distance between the open inner ring and the open outer ring of the improved SRR structure is larger than 0.5mm, so that electromagnetic coupling is avoided.

As the preferable technical scheme, a defected ground structure is adopted, and the metal with the length of 10mm and the width of 9mm in the middle of the ground plane is hollowed, so that the coupling of the SRR structure is avoided and improved.

As a preferred technical scheme, the PDMS is used for manufacturing the micro-fluidic channel, and the material has the advantages of electrical insulation, hydrophobicity, high shearing resistance and relatively convenient processing, so that the material is the best choice for manufacturing the fluidic channel. The manufactured fluid channel is a curved and folded cuboid, the cross section area of the fluid channel is 0.15mm multiplied by 0.2mm, the total length of the fluid channel is about 17mm, and the fluid channel can occupy the position of strong electric field intensity in the maximum range, so that the change of reflection characteristics is the maximum, and meanwhile, the measured liquid is not wasted.

As the preferable technical scheme, the improved SRR structure is printed on the upper layer of the dielectric plate, and the capacitance polar plate and the interdigital capacitance are added into the improved SRR structure to increase the capacitance of the sensor, and the inner ring of the improved SRR structure adopts the traditional rectangular structure, so that the highest electric field intensity is conveniently obtained by optimization.

As a preferable technical scheme, the signal input microstrip line is directly connected with the capacitance polar plate of the improved SRR structure, and the proper width of the signal input microstrip line is selected so as to maximize the resonance depth, thereby better representing the dielectric constant imaginary part of the liquid to be measured.

As a preferred solution, the improved SRR structure constitutes a resonant circuit. The resonant frequency of the SRR is dependent on the inductance and capacitance of the improved SRR structure as a whole, and the specific expression is as follows:

when the liquid to be measured is introduced into the fluid channel, the overall resonant frequency of the resonant circuit changes, mainly in that the capacitance part is no longer entirely dependent on the capacitance of the modified SRR structure itself, but the capacitance with the liquid to be measured also has a correlation. The specific expression is as follows:

wherein L is _p 、C _p Respectively, the inductance and capacitance of the improved SRR structure. C (C) _LUT The change in sensor capacitance when the liquid to be measured is added to the sensor is simulated.

The sensor is used for extracting the dielectric constant of the measured liquid, so that it is important to improve the sensitivity of the sensor. Sensitivity is defined as:

wherein Δf _z Is the shift in resonant frequency and delta epsilon is the change in dielectric constant of the dielectric sample loaded on the resonator. When the liquid under test is loaded into the fluid channel, it is equivalent to adding an additional capacitor to the sensor (only the real dielectric constant will be discussed here). The above formula can be used to obtain:

wherein Δεand C _LUT Is determined by the physical characteristics of the liquid being measured. However, f _z And C _p Determined only by the physical characteristics of the sensor. Thus, in designing the sensor, f _z And C _p Is the key to control sensitivity. It is not difficult to find that when f _z And C _p When increased, the sensitivity also increases. However, at increasing f _z In this case, it is necessary to consider the increase in the measurement difficulty and the processing difficulty. At the elevation of C _p When considering the sensitivity effect of the low electric field strength SRR outer loop portion capacitance, it is necessary. Thus, the present deviceThe meter obtains the proper f through various considerations _z And C _p The value has a certain improvement on the measurement sensitivity.

Compared with the prior art, the utility model has the following technical effects:

1. the utility model adopts the SRR structure to replace the CSRR structure in the traditional micro-fluid sensor to realize the no-load resonance frequency of the sensor of 3GHz, and the signal input microstrip line is directly connected with the capacitance polar plate of the improved SRR structure, thereby greatly reducing the size of the sensor, and simultaneously increasing the capacitance of the improved SRR structure to reduce the working frequency, and facilitating the measurement. The use of the defected ground structure eliminates the improvement of the coupling capacitance of the SRR structure and the ground plane metal, enhancing the sensitivity. The interdigital capacitor can increase the capacitance under the condition of unchanged size, further reduces the size of the sensor, reduces the amount of liquid to be measured consumed by measurement, and is an almost noninvasive microfluidic sensor.

2. The utility model can be applied to the aspect of medical biology and is used for detecting the dielectric constant of the tested liquid, and the concentration of the tested liquid is reversely deduced through the dielectric constant. Compared with the traditional utility model, the sensitivity of the utility model is greatly improved, the consumption of the tested liquid is very little, and the utility model can play a good role in practical application.

Drawings

Fig. 1 is a schematic diagram of the working principle of the microwave sensor for measuring complex dielectric constant of liquid according to the present utility model.

FIG. 2 is a schematic diagram of the structure of a microwave sensor for liquid complex permittivity measurement according to the present utility model;

FIG. 3 is a top view of a sensor based on an improved SRR structure in accordance with a preferred embodiment of the present utility model;

FIG. 4 is a bottom view of a sensor based on a modified SR R structure in a preferred embodiment of the utility model;

FIG. 5 is a diagram of an equivalent circuit model of a preferred embodiment of the present utility model;

fig. 6 is an electric field distribution at an idle transmission response and resonant frequency of the present utility model;

FIG. 7 is the reflectance of an ethanol-water binary solution for different water volume fractions for an SRR-based sensor of the present utility model;

FIG. 8 is a graph comparing actual values of relative dielectric constants of an ethanol-water binary solution of the present utility model with values measured using a design sensor;

Detailed Description

The following are specific embodiments of the present utility model and the technical solutions of the present utility model will be further described with reference to the accompanying drawings, but the present utility model is not limited to these embodiments.

The utility model aims at the defects of the prior art microwave sensor and aims at improving the sensitivity and non-invasiveness of the microwave sensor. The idle frequency of the microwave sensor is also a first concern. The selection of the idle frequency is firstly to make the measurement more convenient, i.e. the measurement can be carried out by using a lower-priced instrument. Secondly, the idle frequency has a great influence on the size of the circuit board and also has a certain influence on the sensitivity. Therefore, the frequencies should be chosen to be less than 3GHz and greater than 2GHz, which does not result in excessive board size, nor can the product be suitable for most vector network analyzers. The selection of a suitable resonator structure is critical to the various sensor specifications. More CSRR and SIR structures are currently used. The present utility model selects a novel SRR architecture. The largest difference between the SRR structure and the CSRR structure is that the CSRR structure is a defective ground structure, a microstrip line for transmitting signals is positioned above a dielectric plate, the signals need to be transmitted through coupling, the SRR structure is directly printed on the dielectric plate and connected with a signal input/output microstrip line, so that signal attenuation is reduced, and the imaginary part change of dielectric constants is facilitated to be observed. On the other hand, the main source of the inductance of the improved SRR structure is the narrow microstrip line of the open outer ring, and the capacitance is mainly derived from the capacitance polar plate loaded by the improved SRR structure and the interdigital capacitance added in the capacitance polar plate, so that the capacitance of the improved SRR structure is greatly increased. Therefore, under the same size, the size of the SRR structure in the design is far smaller than that of the traditional CSRR structure and SIR structure, which accords with the trend of miniaturization of modern devices, namely, the SRR structure saves materials and is convenient to carry.

Based on the design consideration, the utility model provides a microwave sensor for measuring the complex dielectric constant of liquid, referring to fig. 1, which is a schematic diagram of the measurement principle, a simple vector network analyzer is used to connect two ends of the microwave sensor with two ports of the sensor respectively, input small-power signals, fix the connection wires and prevent the movement of the transmission line from influencing the measurement. Then, the liquid to be measured is injected into the PDMS fluid channel using an injector, and the injection must be slow and stable to prevent leakage of the liquid to be measured. Different resonant frequencies and resonant depths can be extracted according to S21 displayed by the vector network analyzer, so that complex dielectric constants of liquid to be measured can be reversely represented.

Referring to fig. 2, a three-dimensional view of a microfluidic sensor with PDMS microfluidic channels according to an embodiment of the present utility model at least includes a dielectric plate, a resonator disposed on an upper layer of the dielectric plate, a signal input microstrip line and a signal output microstrip line electrically connected to the resonator, and a PDMS fluidic channel disposed on the resonator, wherein the signal input microstrip line is provided with a port 1 for inputting a measurement signal; the resonator is used for generating a resonance signal according to an input signal, wherein a modified SRR structure is adopted as a sensing area to provide a basic resonance signal, and the resonance signal has corresponding resonance frequency and resonance depth under the disturbance of liquids with different dielectric constants; the PDMS fluid channel is used for stably injecting liquid to be detected with different dielectric constants into the sensing area; the signal output microstrip line is provided with a port 2 for outputting a resonance signal, and the resonance frequency and the resonance depth generated by the liquid to be measured are obtained through the resonance signal, so that the complex dielectric constant of the liquid to be measured is obtained.

The improved SRR structure at least comprises a capacitor plate, an interdigital capacitor, an open outer ring and an open inner ring, wherein one side of the open outer ring is provided with a gap, two opposite capacitor plates are arranged at the gap and are respectively and directly electrically connected with the signal input microstrip line and the signal output microstrip line, and the interdigital capacitor is arranged between the two capacitor plates.

As a further improvement, the signal input microstrip line and the signal output microstrip line are directly connected with the capacitor plate of the improved SRR structure. Wherein the microfluidic channel is fabricated using PDMS. PDMS has electrical insulation, hydrophobicity, high shear resistance and convenient processing. Is the best choice for making the fluid channel. The fluid channel was manufactured as a curved and folded rectangular parallelepiped with a cross-sectional area of 0.15mm by 0.2mm and a total length of the fluid channel of about 17mm.

In the technical scheme, the improved SRR structure is directly connected with the signal input and output microstrip lines, so that the generation of coupling capacitance between the improved SRR structure and the signal transmission microstrip lines is avoided, interference capacitance is reduced, the sensitivity of the sensor is improved, and the size of the sensor is reduced; meanwhile, a capacitor polar plate is added in the improved SRR structure to directly generate capacitance required by resonance, and an outer ring of the improved SRR structure is used to generate inductance required by resonance, so that the overall size of the sensor is reduced; in addition, the interdigital capacitor structure is used for greatly increasing the capacitance of the improved SRR structure under the condition of unchanged overall size, so that the no-load resonance frequency of the sensor is smaller than 3GHz, the measurement can be carried out in a common network analyzer, and the measurement cost is reduced; the use of the defected ground structure avoids the improvement of the interference capacitance created between the SRR structure and the ground plane metal, further increasing the sensitivity of the sensor.

The conventional SRR structure consists of two annular metal grooves printed on one metal plate. Referring to fig. 3, which is a top view of a sensor based on a modified SRR structure in a preferred embodiment of the present utility model, the modified SRR structure used in the present utility model is different from the conventional SRR and CSRR structure, and in a preferred design of the present utility model, the modified SRR structure is directly connected to the microstrip line through a capacitor plate at a gap of a loop, that is, the SRR in the design of the present utility model is an open resonator, whereas the conventional SRR and CSRR are closed resonators, and when applied to a sensor, the CSRR needs to be coupled with the microstrip line, which causes loss during signal transmission, whereas the modified SRR structure does not have the problem. In addition, the improved SRR structure is loaded with the capacitor polar plate and the interdigital capacitor is added, so that the capacitor of the resonator can be increased under the condition of the same size, and meanwhile, after the liquid to be detected is injected, the capacitor can also be greatly changed due to the large quantity of the interdigital capacitors, so that the sensitivity loss cannot be caused by the increase of the capacitor of the resonator of the improved SRR structure. The rectangular inner ring of the SRR facilitates position adjustment to obtain maximum electric field concentration. Since the main source of the inductance of the improved SRR structure is the narrow microstrip line of the open outer loop, and the capacitance is mainly derived from the capacitive plates loaded by the improved SRR structure and the interdigital capacitance added in the capacitive plates, the capacitance of the improved SRR structure is greatly increased. Therefore, under the same size, the size of the SRR structure in the design is far smaller than that of the traditional CSRR structure and SIR structure, which accords with the trend of miniaturization of modern devices, namely, the SRR structure saves materials and is convenient to carry. Thus, the open improved SRR architecture is more suitable for use in fabricating microwave sensors than the CSRR architecture. In this embodiment, s1 and s2 are set to different values, and there is a certain improvement in sensitivity.

Referring to fig. 4, which is a bottom view of a sensor of an improved SRR architecture according to a preferred embodiment of the present utility model, it can be seen from the bottom surface of the sensor that the defected ground structure is a metal of 10mm length and 9mm width in the middle of the ground plane, which effectively eliminates the coupling capacitance between the improved SRR architecture and the ground plane metal, further increasing the sensitivity of the sensor.

Referring to fig. 5, an equivalent circuit model diagram of the present embodiment is shown. Wherein L is ₁ Representing the inductance of the metal strip connecting the signal input output microstrip line of the modified SRR structure. L (L) _P 、C _P Respectively, the inductance and capacitance of the improved SRR structure. L (L) ₂ Representing parasitic series inductance of two capacitive plates, and C ₁ The coupling capacitance between the ground plane with two incompletely hollowed ends and the signal input/output microstrip line is represented, and the coupling capacitance has a small value and has weak influence on sensitivity, so that the coupling capacitance can be ignored for the sake of simplicity of calculation. Since the influence of the resistance on the resonance frequency is not large, the resistance is not considered in the circuit equivalent model. The improved SRR structure forms a resonant circuit, and the resonant frequency of the resonant circuit depends on the inductance and capacitance of the overall improved SRR structure, and is expressed as followsThe following steps:

when the liquid to be measured is introduced into the fluid channel, the overall resonant frequency of the resonant circuit changes, mainly in that the capacitance part is no longer entirely dependent on the capacitance of the modified SRR structure itself, but the capacitance with the liquid to be measured also has a correlation. The specific expression is as follows:

wherein L is _p 、C _p Respectively, the inductance and capacitance of the improved SRR structure. C (C) _LUT The change in sensor capacitance when the liquid to be measured is added to the sensor is simulated. Thus, when liquid samples of different dielectric constants are added, the resonators of the SRR structure will produce different resonant frequencies. The dielectric constant of the liquid sample can be reduced by measuring the resonant frequency.

In addition, the sensor is used for extracting the dielectric constant of the measured liquid, so that it is very important to improve the sensitivity of the sensor. The sensitivity of the sensor is defined as:

where Δf is the shift in resonant frequency and Δε is the change in dielectric constant of the dielectric sample loaded on the resonator. When the liquid under test is loaded into the fluid channel, it is equivalent to adding an additional capacitor to the sensor (only the real dielectric constant will be discussed here). The above formula can be used to obtain:

wherein Δεand C _LUT Is determined by the physical characteristics of the liquid being measured. However, f _z And C _p Determined only by the physical characteristics of the sensor. Thus, in designing the sensor, f _z And C _p Is the key to control sensitivity. It is not difficult to find that when f _z When increased, the sensitivity also increases. However, at increasing f _z In this case, the measurement and manufacturing difficulties need to be considered. When C _p The sensitivity increases as it decreases. However, in reducing C _p We consider the effect of the decrease in electric field strength on the measurement. Suitable f _z And C _p It is advantageous to achieve maximum sensitivity.

Referring to fig. 6, which shows the idle transmission response and the electric field distribution at the resonance frequency of the present embodiment, it can be found that there is a very dense electric field strength in the vicinity of the portion of the interdigital capacitor in the modified SRR structure, up to 60000v/m. Thus, placing the fluid channel in this position maximizes sensitivity.

Referring to fig. 7, the reflection coefficients of the SRR based sensor of the present embodiment for ethanol-water binary solutions of different water integral numbers are shown. It can be seen that when the concentration of water in the ethanol-water binary solution is gradually reduced, the resonance frequency is gradually reduced from 1.71GHz to 0.7GHz, the overall resonance frequency is close to 1000MHz, and the sensitivity is extremely high.

Referring to fig. 8, a graph showing a comparison between actual values of relative dielectric constants of the ethanol-water binary solution and values measured using the design sensor according to the present embodiment is shown. It can be seen from the figure that the relative permittivity of the reduced ethanol-water binary solution from this example is very close to the actual value and can be used for actual measurement. The present example finally achieves that only 0.5 μl of the liquid under test is used for each measurement, and achieves a maximum variation in the 990MHz resonant frequency, achieving an average sensitivity of 1.8%. Compared with the existing microwave sensor, the design has great advantages in sensitivity and consumption of liquid samples. By testing the sensor designed by the utility model, the experimental result is well matched with the simulation result. The sensitivity of the sensor is greatly higher than that of the existing similar sensor and is as high as 1.8%, and the quantity of the liquid to be measured consumed by measurement is far less than that of the existing similar sensor. Has great practical potential in the aspect of complex dielectric constant characterization.

In order to solve the technical problems in the prior art, the utility model also provides a design method of the microwave sensor for measuring the complex dielectric constant of the liquid, which at least comprises the following steps:

step S1: forming an improved SRR structure on the upper layer of the dielectric plate and removing metal right below the improved SRR structure to form a defective structure; the improved SRR structure at least comprises a capacitor plate, an interdigital capacitor, an open outer ring and an open inner ring, wherein one side of the open outer ring is provided with a gap, two opposite capacitor plates are arranged at the gap and are respectively and directly electrically connected with the signal input microstrip line and the signal output microstrip line, and the interdigital capacitor is arranged between the two capacitor plates;

step S2: bonding a PDMS fluid channel on the modified SRR structure for introducing and emptying the tested liquid;

step S3: the signal transmission circuit is designed and comprises a signal input microstrip line and a signal output microstrip line, wherein the signal input microstrip line and the signal output microstrip line are directly connected with a capacitor polar plate in the improved SRR structure to finish the access and output of signals;

step S4: injecting a liquid to be tested into the PDMS fluid channel by using an injector so as to change the dielectric parameter of the improved SRR structure;

step S5: the signal input microstrip line inputs a signal, the measurement signal outputs an output signal of the microstrip line, wherein the improved SRR structure generates an S parameter signal according to a measured fluid flowing through a fluid channel on the improved SRR structure, the resonance frequency of the S parameter is used for representing the real part of the dielectric constant of the liquid to be measured, and the resonance depth is used for representing the imaginary part of the dielectric constant of the liquid to be measured, so that the complex dielectric constant of the liquid to be measured is obtained.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present utility model, and not for limiting the same; although the utility model has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the utility model.

Claims (9)

1. The microwave sensor for measuring the complex dielectric constant of the liquid is characterized by at least comprising a dielectric plate, a resonator arranged on the upper layer of the dielectric plate, a signal input microstrip line and a signal output microstrip line which are electrically connected with the resonator, and a PDMS fluid channel arranged on the resonator, wherein the signal input microstrip line is provided with a port 1 for inputting a measurement signal; the resonator is used for generating a resonance signal according to an input signal, wherein a modified SRR structure is adopted as a sensing area to provide a basic resonance signal, and the resonance signal has corresponding resonance frequency and resonance depth under the disturbance of liquids with different dielectric constants; the PDMS fluid channel is used for stably injecting liquid to be detected with different dielectric constants into the sensing area; the signal output microstrip line is provided with a port 2 for outputting a resonance signal, and the resonance frequency and the resonance depth generated by the liquid to be measured are obtained through the resonance signal, so that the complex dielectric constant of the liquid to be measured is obtained.

2. The microwave sensor for liquid complex permittivity measurement according to claim 1, wherein the improved SRR structure at least comprises a capacitor plate, an interdigital capacitor, an open outer ring and an open inner ring, wherein one side of the open outer ring is provided with a gap, two opposite capacitor plates are arranged at the gap and are respectively and directly electrically connected with the signal input microstrip line and the signal output microstrip line, and the interdigital capacitor is arranged between the two capacitor plates.

3. The microwave sensor for liquid complex permittivity measurement according to claim 2, characterized in that the PDMS fluid channel is arranged directly above an interdigital capacitance.

4. A microwave sensor for liquid complex permittivity measurement according to claim 2 or 3, wherein the PDMS fluid channel is made of polydimethylsiloxane material and has a rectangular parallelepiped structure, including PDMS colloid, a hollow channel of the fluid channel, and an in-out cylindrical injection port.

5. The microwave sensor for liquid complex permittivity measurement according to claim 4, wherein a defective ground structure is provided on the lower layer of the dielectric plate, and metal directly under the modified SRR structure is removed to avoid capacitance between the modified SRR structure and the ground plane.

6. The microwave sensor for liquid complex permittivity measurement according to claim 4, wherein the distance between the open inner ring and the open outer ring in the modified SRR structure is greater than 0.5mm.

7. A microwave sensor for liquid complex permittivity measurement according to claim 5, wherein the defected ground structure is hollowed out of metal of length 10mm and width 9mm at the midpoint of the ground plane.

8. The microwave sensor for liquid complex permittivity measurement according to claim 5, wherein the manufactured fluid channel is a curved folded rectangular parallelepiped having a cross-sectional area of 0.15mm x 0.2mm, and a total length of the fluid channel is 17mm.

9. A microwave sensor for liquid complex permittivity measurement according to claim 2, characterized in that the modified SRR structure constitutes a resonant circuit whose resonant frequency depends on the inductance and capacitance of the modified SRR structure as a whole, expressed by the following expression:

when the liquid to be measured is added into the fluid channel, the overall resonant frequency of the resonant circuit changes, wherein the capacitance part is not completely dependent on the capacitance of the improved SRR structure, and the capacitance of the liquid to be measured is related to the capacitance of the liquid to be measured, and the specific expression is as follows:

wherein L is _p 、C _p Respectively representing the inductance and capacitance of the improved SRR structure; c (C) _LUT Simulating a change in sensor capacitance when the liquid to be measured is added to the sensor;

the sensor sensitivity is defined as:

wherein Δf _z Is the shift in resonant frequency, delta epsilon is the change in dielectric constant of the dielectric sample loaded on the resonator; when the liquid to be measured is loaded into the fluid channel, it is equivalent to adding an additional capacitor C to the sensor _LUT The method comprises the steps of carrying out a first treatment on the surface of the The above formula can be used to obtain:

wherein Δεand C _LUT Is determined by the physical characteristics of the measured liquid, f _z And C _p Determined only by the physical characteristics of the sensor; through f _z And C _p Is the control sensitivity; when f _z And C _p When increased, the sensitivity also increases.